Some Observations on the Behaviour of Amoeba proteus.

<strong>Some</strong> <strong>Observations</strong> on the Behaviour of 

Amoeba proteus. 

By 

C. W. Parsons, B.A., 

Department of Zoology, University of Glasgow. 

With 9 Text-figures. 

ALTHOUGH the body-form of Amoeba proteus shows 

so much diversity in any healthy culture, the differences that 

may be observed conform to certain types. If these are 

assembled, they fall into groups which may be supposed to 

indicate physiological variation in the organisms ; for they 

are then reacting in different ways to the stimuli provided by 

the same external medium, and such behaviour can best be 

explained on physiological bases. 

The investigation of the groups is approached in the following 

pages by two different routes. The first is experimental and 

consists in a re-examination of the normal behaviour of adult 

Amoebae in the aquarium medium in which they are best 

cultured (see Monica Taylor, 11), followed by an analysis of 

their reactions to simple changes in their environment. The 

second is deductive. It rests upon a hypothesis relating the 

degree of activity of these organisms, as measured by the 

rapidity and ease with which they extend their pseudopodia, 

with their health. It recognizes the presence of healthy forms, 

in unfavourable as well as in favourable environments, and puts 

forward the view that some Amoebae are more adaptable to 

change of medium than are others. A link is here established 

with the well-known fact that while the Amoebae in a culture 

cease to reproduce by fission after a time, many of them do not 

enter on the cycle of encystment. They die out for no obvious

630 C. W. PARSONS 

reason. Food remains abundant, overcrowding is avoided, and 

the pH throughout the culture may be adjusted to give conditions 

normally ideal for multiplication. The attempt is here 

made to correlate this peculiarity in life history with a conspicuous 

variation in body-form, and the types exhibiting this 

variation are defined. 

Material.—Adult Amoebae having chromosome blocks in 

the periphery of their nuclei, from a nourishing sub-culture of 

Dr. Monica Taylor's culture ' 19 ', type ' B ' (12, pp. 187 and 

120). 

Apparatus included — plunger pipettes, i.e. capillary 

pipettes fitted internally with drawn-glass rods and sealed with 

rubber tubing. (See Brooker Klugh, 5.) 

Solid watch-glasses, 1| in. square; J in. deep for supporting 

cover-slips in high-power work ; ^ in. deep for general purposes. 

Sarensen phosphate buffer solutions with indicators, made 

up to 10 e.c. and 2 c.c. 

A. Behaviour of Adult Amoebae in Culture 

Media free from Debris. pH 6-8. 

The Amoebae are readily seen as white specks if debris containing 

them is taken from the parent culture and placed in 

a shallow dish on a black background. They may be picked 

up singly with the plunger pipette and transferred for observation 

to a solid watch-glass containing clean culture medium. 

If there is rather less than 2 c.c. of fluid they may be focussed 

with a Zeiss ' A ' objective (f in.), and their behaviour recorded 

by notes and drawings taken at suitable intervals. 

High-power observation of single living Amoebae in a drop 

of fluid was carried out on a clean glass cover-slip supported in 

the well of one of the very shallow watch-glasses (£ in. deep). 

If the drop of fluid is small, the Amoebae may be focussed with 

a Zeiss ' D ' objective (£ in.), and the drop can be renewed as 

required from a fine-drawn pipette. When set aside, rapid 

evaporation may be prevented by placing another solid watchglass 

on top of the one already holding the cover-slip, and the 

Amoebae remain alive in the drop.

BEHAVIOUR OF AMOEBA 631 

When they are picked up with the plunger pipette the 

Amoebae withdraw their pseudopodia, and it thus comes about 

that they are delivered to the solid watch-glasses as rounded 

masses of protoplasm. If they are kept floating—by gentle 

agitation of the fluid—they extend numerous blunt pseudopodia 

(Text-fig. 1). When allowed to settle, however, they 

adhere to the glass surface in an orderly fashion. First, one 

of the pseudopodia reaches the substratum and adheres to it by 

TEXT-FIGS. 1, 2. 

Tig. 1.—Typical body-form of a floating Amoeba proteusinits 

aquarium culture medium. The figure shows a radial disposition 

of pseudopodia of roughly equal size. 

Fig. 2.—Contact with the substratum is first established by adhesion 

to it of one of the radial pseudopodia, which is distinguishable 

now as the major pseudopodium. 

the tip. Then it receives the remaining protoplasm (Textfigs. 

2, 3, and 4) and, leading the organism down to the substratum, 

it becomes the directive pseudopodium in the new line 

of advance. The Amoebae adhere closely to the glass surface 

as a rule, and move rapidly over it in a digitate form. A broader 

extremity crowned with active pseudopodia lies in the main 

axis of advance, and a slight constriction commonly marks the 

' tail' (Text-fig. 4, t). 

The ' tail ' is a conspicuous feature of most Amoebae even 

in experimental media. It is seldom the seat of pseudopodia


formation, a point which is emphasized by observing theeffect 

of mechanical stimulation upon one of these adheringforms 

in culture medium. Schaeffer has shown how they 

respond when a glass needle is agitated near to them by initiating 

the ' feeding mechanism' (10, p. 229), but if the medium isdisturbed 

in this way immediately in front of the advancing 

pseudopodia, an avoiding reaction is induced. The flow of 

TEXT-FIGS. 3, 4. 

Fig. 3.—Further stage in the transition from a floating condition 

to one of adherence to the substratum. 

Fig. 4.—A completely adherent active Amoeba of the type shown 

floating in Text-fig. 1, with a body-form frequently observed, 

comprising three main pseudopodia, an elongate body, and a 

slightly constricted ' tail' (t). Same scale as fig. 1. 

granules is at first arrested and then reversed. After receding' 

a little, the Amoeba moves away afresh at an angle less than 

a right angle from its previous direction of flow. If now left 

undisturbed the pseudopodia gradually deflect into the original 

alinement and draw the animal into a path parallel to but 

slightly removed from its former course. On the other hand, 

this movement may be checked soon after its commencement 

by disturbing the medium again in front of the pseudopodia 

when they begin to diverge. The original course is then


reversed : not, however, by the formation of pseudopodia 

at the hinder end, but by movement of lateral pseudopodia into 

the new position which draw the ' tail' round after them. This 

behaviour is typical of the most active adult Amoebae in culture 

media. 

Many adult Amoebae prove to be relatively inactive when 

taken from the parent culture. They are frequently more 

consolidated than the more active forms and may be very much 

shrunken. There seems, in fact, to be a gradation between 

the most active and least active Amoebae, marked by a change 

in their appearance under transmitted light from grey to black. 

It is notable also that the darker forms tend to lose their 

adhesion to the sides of the vessel containing them with greater 

ease than do the active grey ones. This suggests that granularity 

and adhesiveness on the one hand, and readiness of 

movement on the other, may be complementary features. 

B. Behaviour of Amoeba proteus in Pure Media. 

The water used in the following observations was distilled 

once from Glasgow tap-water in a glass condensing apparatus. 

A little potassium permanganate and a trace of mineral acid 

was added before distillation to oxidize impurities. The 

distillate, called hereunder glass distilled Avater, had a steady 

pH of 5-8 before prolonged exposure to the atmosphere. 

The Amoebae may reasonably be separated into three types 

on the basis of their reactions to this medium. 

1. The majority quickly extend numerous pseudopodia to 

relatively great distances. (Text-fig. 5.) The reaction is the 

same in well-aerated distilled water, and has no relation therefore 

to the recognized paucity of oxygen in untreated glass distilled 

water. On theoretical grounds Mr. C. F. A. Pantin informs me 

that the ratio of surface to volume in Amoeba is so great, that 

equilibration with oxygen in the external medium is effected 

in an extremely short space of time. The small increase of 

surface produced therefore by great extension of pseudopodia, 

will not avail to compensate for a law oxygen content in the 

medium; although of course the great variation in ' per-


nieability ' of living protoplasm to oxygen is not disputed 

(cf. ' Air-bladder of Fishes '). 

TEXT-FIG. 5. 

The exaggerated floating Jorm ot an active Amoeba suspended in 

distilled water. The attenuated pseudopodia suggested the distinction 

of Amoebae that react in this way from others which are 

less active, and it was convenient to describe them as type ' A ' 

Amoebae. 

Amoebae in glass distilled water do not, as a rule, fix themselves 

to the substratum. They float with extended pseudopodia 

in a most grotesque manner, and are extremely active


at first. Their energy is slowly dissipated, however, and in 

8-10 hours they become sluggish. As time elapses they shrink 

and grow darker in appearance, but they may remain alive 

5-7 days before cytolysis. The death of the organism is frequently 

preceded by its assumption of a more or less spherical 

form in accordance with its subjection to the ordinary forces 

of surface tension. Distension of its outer layers—owing to the 

decrease in efficiency of the contractile vacuole which normally 

Illustrates a body-form not infrequently observed amongst active 

Amoebae that are floating in pure media. Movement is steadily 

maintained in the outer layers, which may therefore differentiate 

sharply as at a, from the endoplasm. Movement in the latter is 

also vigorous, but it is checked periodically and results in exceptionally 

blunt pseudopodia, b. Same scale as fig. 1. 

counteracts the diffusion of water into the Amoeba may be 

observed, and the appearance then presented is that of a very 

large vacuole with a small quantity of granular cytoplasm about 

it. After this has been realized, the actual cytolysis may be 

delayed for a period varying in individual cases between a clay 

and only a few hours. If returned to culture medium within 

the first 8 hours, or during their active phase, the Amoebae 

recover rapidly and completely : but if this is delayed until 

they have become sluggish, recovery is partial and gives rise 

to dark, slow-moving forms in the majority of cases. 

A noticeable variation in the ease with which the elongated 

pseudopodia are extended, is to be seen in these experiments..


Movement in some Amoebae proceeds jerkily. At a, Textfig. 

6, a narrow streak of the clear outer layer is put forward, 

while the flow of granules goes on in the cytoplasm behind it. 

The granules accumulate in great numbers as a result and 

swell out the ectoplasm about them into ' beads '. These 

disperse suddenly when the pressure releases, to form exceptionally 

blunt pseudopodia (b, Text-fig. 6). This type of bodyform 

is described by Gruber (3, p. 256), with the suggestion that 

it indicates abnormal consolidation of the outer surface layers. 

TEXT-FIG. 7. 

The poor response to cuange in environment or one of the darker 

inactive Amoebae that occur in culture media, illustrated by the 

ragged appearance of 6ne of them in distilled water. It is a typical 

type ' R ' Amoeba. Same scale as fig. 1. 

2. The darker inactive Amoebae, which have already been 

mentioned because they occur in culture media, do not respond 

so well to the stimulus of glass distilled water. Only short 

pseudopodia are extended when they are transferred to this 

fluid. The outer layers are abnormally distinct in them, and 

they float with very ragged outlines and limited powers of 

movement. (Text-fig. 7.) 

3. Exceptional Amoebae remain. These rare forms make no 

response at all to the alteration in environment. They are 

typically clavate, and adhere lightly to the substratum in 

culture medium. In distilled water they retain this capacity 

to some extent. (Text-fig. 8.)


When these forms are contrasted, the desirability of splitting 

the active and inactive groups into types is apparent. 

Active attenuating forms . . type ' A ' (Text-fig. 5). 

Inactive ragged forms . . type ' E ' (Text-fig. 7). 

Inactive clavate forms . . type ' C ' (Text-fig. 8). 

The types ' E ' and ' 0 ' are more abundant in cultures wherein 

multiplication of Amoebae by fission has been in full progress 

TEXT-FIG. 8. 

A clavate irresponsive form of Amoeba, which is rare in culture 

media, figured from distilled water; the type ' C ' Amoeba. 

for many months. This, correlated with the fact that type ' A ' 

Amoebae from these cultures are less responsive to the immediate 

effects of distilled water, suggests that somewhat unfavourable 

conditions hasten the change from type ' A ' to type ' E '; 

which under normal vigorous circumstances will proceed very 

slowly. This does not mean that the types ' E ' and ' C ' are 

absent from the most flourishing cultures. They may be found 

in them, but are rare.


In glass distilled water containing measurable traces of acid 

or base, Amoebae react in a manner emphasizing the above 

point with regard to unfavourable conditions. Their behaviour 

in these solutions is influenced by four factors : 

1. The type of Amoeba, ' A ', ' E ', or ' C '. 

2. The duration of experiment. 

3. The acid or base employed. 

4. The change in pH involved in transferring the Amoebae 

from the culture medium to the artificial medium. 

1, 2, and 3 may be controlled by selection ; 4 requires an 

adjustment of the pH of the artificial medium, which may be 

carried out by the following process : 10 c.c. of glass distilled 

Avater are measured from a burette into each of a dozen clean 

test-tubes. Ten drops of the indicator proper to the desired 

range of pH follow in the concentration given in Clark and 

Lubs's list of indicators (2, p. 80), and drops of a very dilute 

solution of the pure acid or base selected for experiment. 

Any one colour given in the same amount of phosphate mixture 

by the same indicator can thus be accurately matched, and the 

pH of the Avater in the test-tubes is standardized. If the number 

of drops of the acid or alkaline solution required to obtain a 

desired pH exceeds five, a slightly stronger solution should be 

employed. 

It was at first desirable to use experimental media free from 

indicators. The number of drops of acid or base at the giA 7 en 

dilution necessary to bring 10 c.c. of glass distilled water to the 

desired pH Avas calculated by this method, therefore, and then 

added to 10 c.c. of fresh distilled water. The pH of the resulting 

solution was checked by removing 2 c.c. of it, adding 2 drops of 

indicator, and comparing the colour obtained with that of 2 c.c. 

of phosphate mixture with indicator. It was found, hoAvever, 

that the presence of so small a quantity of indicator made 

little difference to the behaviour of the Amoebae. 

It is not possible to maintain a standardized pH for long 

observation in the region of the neutral point. In dealing Avith 

alkali, for example, media in the absence of buffering salts 

readily absorb CO 2 and other acid gases from the atmosphere,

BEHAVIOUR OP AMOEBA 639 

and tend to become less alkaline with increasing rapidity as the 

pH decreases. This can only be partially remedied by basing 

every judgement on a number of observations, by renewing the 

fluid as often as possible, by recording the pH before and after 

each experiment, and by making up such solutions in glass 

distilled water that has been exposed to the atmosphere until 

the pH has risen to some steady point. In the Glasgow laboratory 

it commonly rises from 5-8 to 6-2. 

For comparison, the records of the behaviour of the Amoebae 

over a definite range of pH are best obtained simultaneously. 

A number of solid watch-glasses are placed under microscopes 

accommodating the solutions of different pH, and to each are 

then added four or five Amoebae. These are selected from 

distilled water according to the type required, and transferred 

to the solid watch-glass after a preliminary wash in the experimental 

solution. If the experiments are started at 20 min. 

intervals, a general idea of the behaviour of the Amoebae in 

each watch-glass is gathered by observing them continuously 

for the first 15 min., and afterwards at intervals determined by 

their activity. A wide range of pH cannot of course be 

attempted. Six values are about the maximum that may be 

covered, and even then it is barely possible to give the necessary 

attention to the six microscopes when the whole series is under 

observation. 

The results of such observation, covering a period of one hour 

for each watch-glass, are given in Text-fig. 9. The degree of 

attenuation of the pseudopodia, which attains a maximum in 

this time as a rule, is expressed by the size of the crosses. The 

pHs of the experimental solutions are given in the horizontal 

row of figures, and in this instance the Amoebae selected were 

of the type ' A ' after a short immersion in distilled water— 

pH 5-8. It is important to emphasize the fact that they were 

derived originally from a culture of pH 6-8 ; for Amoebae 

flourish in cultures considerably more acid and more alkaline 

than this, and their behaviour in the experimental solutions 

is determined by the extent of the contrast between the pH 

of the culture and that of the solution to which they are trans- 

NO. 280 

U U


ferred. If returned to the culture medium at the end of an 

hour, Amoebae that have not been brought to the point of 

maximum attenuation recover rapidly and completely. 

Eecovery is also possible beyond this point over the range of 

pH covered by the diminishing crosses in Text-fig. 9 ; but it 

then gives rise to forms which approximate to the types 

' E' and ' C', and the changes are not therefore completely 

reversible. 

If the period of immersion in an experimental solution is prolonged, 

recovery becomes progressively less possible. The 

Amoebae die in the more acid and more alkaline solutions within 

the first 5 hours. In the less abnormal solutions they become 

sluggish and consolidated in the same way as they do when 

floating in distilled water, and will make a partial recovery if 

returned to culture medium while movement of granules in 

their endoplasm can still be traced. The time when such movement 

ceases and when the changes become irreversible varies 

with the acid or base employed, and, to some extent, with the 

individual resistance of each Amoeba. In acid solutions there 

is a tendency for this time to be marked by local distensions 

of the outer layers, which give to an Amoeba a ' beaded ' 

appearance. In some alkaline solutions, e. g. sodium hydroxide, 

the cessation of all movement is attendant on the formation 

of perfectly spherical bodies ; and in both instances the actual 

rupture of the cell may be delayed two or three days after this 

has happened. Transference to a new medium in this condition, 

however, is almost always followed by immediate cytolysis. 

Ammoniacal solutions, on the other hand, induce cytolysis at 

similar pHs in 4-6 hours, and in them changes involving sudden 

cessation of movement may obviate the possibility of adopting 

a spherical form. 

The reactions of Amoebae belonging to the types ' E ' and 

' C' to these experimental solutions suggest a correlation 

between their reduced surface areas and their lesser irritability. 

There is some attenuation of type ' E ' Amoebae in the early 

stages of immersion, but they round off more readily than do 

the type ' A ' Amoebae. Type ' C ' Amoebae, on the other hand,


remain unaffected until they, in common with the types ' E ' 

and ' A ', round off and cytolize at the higher concentrations 

of acid or base. 

It may be concluded that the effect of these solutions is to 

TEXT-FIG. 9. 

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A representation, by the size of crosses, of the degree of attenuation 

of type ' A ' Amoebae in very dilute pure solutions of various 

acids and bases. 

accentuate the reactions typical of Amoebae to distilled water. 

They are stimulants ; at fairly well-marked critical concentrations 

(pH 4-6 for acetic acid, 4-8 for hydrochloric acid, &c.) they 

become injurious to Amoebae derived from a culture of pH 6-8, 

and their effects are cumulative. <strong>Some</strong> reagents, e. g. ammonia, 

bring about early cytolysis, and with others this occurs after a 

u u 2


variable period of delay. It is also noticeable that the cell 

penetrative fatty acids have a slightly less inhibitory effect upon 

attenuation in type ' A ' Amoebae; an indication, perhaps, that 

they involve in them less radical surface changes. 

DISCUSSION. 

1. Of Adhesion.—It is clear that while the types of 

Amoebae ' A ', ' E ', and ' C ' differ mainly in respect of 

mobility, their behaviour in culture media is further complicated 

by the power they possess of adhering to the substratum. 

When floated in culture media the majority send out spreading 

pseudopodia all round the central mass of protoplasm as in 

Text-fig. 1. In pure media they react in essentially the same 

way (Text-fig. 5), but with excessive attenuation of the pseudopodia 

owing to their abnormal environment. The loss of 

adhesion reveals therefore a characteristic floating form which 

is accentuated in the grotesque appearances presented by the 

floating type ' A ' Amoebae ; and it follows that adhesive 

capacity is an important property of the surface in normal 

healthy Amoebae. The nature of this surface is a matter of 

controversy. It is generally recognized that it cannot be the 

single uniform structure that the term ' ectoplasm ' may be 

held to imply, but there is no general agreement as to the 

nomenclature or structure of the layers that are supposed to 

comprise it. The problem has received the attention of several 

workers who in recent years have studied amoeboid movement, 

either with the view of supplementing the surface tension 

hypothesis, e.g. Schaeffer (9, p. 89), or of replacing it with new 

theories, e.g. Jennings (4), Mast (6), and Pantin (7). Schaeffer 

recognizes a fluid surface tension layer capable of work (9, 

p. 74) over parts of an Amoeba that are not in contact Avith the 

substratum. He explains thus the movement of grains of soot, 

carmine, &c, over the surface of an Amoeba in the direction 

of flow. His hypothesis is supported by experiments with 

type ' A ' Amoebae in water containing particles of washed 

carmine. The grains of carmine adhere to and move over the 

surfaces of Amoebae that are floating in distilled water although


there is a verj' definite loss in them of the capacity for adhering 

to a substratum. <strong>Some</strong> justification may therefore be claimed 

for the conclusion that the mechanism responsible for fixing 

an Amoeba to the substratum is distinct from that by which 

small particles are carried over its surface. The thin tenuous 

layer called by Chambers a ' pellicle ' (1, p. 279) probably 

represents the former, while the latter, a thin fluid film, would 

not be demonstrable separately by microdissection. On this 

hypothesis, the capacity for adhesion depends upon the condition 

of a layer beneath the surface tension layer. Circumstances 

which may render it unusually fluid will impair this 

capacity therefore, and it seems reasonable to assign to such a 

cause the difficulty of inducing adhesion of type ' A ' Amoebae 

in pure media. In active attenuating forms the so-called 

' pellicle ', and any gelating layers associated with it, must be 

in an abnormally fluid condition ; and once they have lost 

from this cause the opportunity of adhesion to the substratum, 

further contact with it is prevented by the buoyancy they 

acquire from their elongating pseudopodia. Conversely, consolidation 

of the outer layers of an Amoeba beyond a certain 

point will also injure its power of adhesion. The types ' B ' and 

' C ' have been described as comparatively immobile forms in 

culture media, and processes of consolidation will therefore 

influence their surface layers for a greater period of time than 

is normally the case. This offers an explanation of a fact of 

behaviour that has been noticed, namely, that these types 

readily lose their adhesion in culture media, and seldom adhere 

to the substratum in pure media although they retain contact 

with it. 

'2. Of Attenuated Pseudopodia.—The remarkable 

activity of type ' A ' Amoebae in pure media directs attention 

to the elongation of their pseudopodia. Schaeffer calls them 

' pseudopodia of position ' to distinguish them from the broad 

pseudopodia of movement seen in normal adhering Amoebae. 

The tendency to adopt a ' radiose ' form was figured by Verwornfor 

Amoeba limax (13, p. 185), and obviously presents 

itself here with the difference that in Amoeba proteus the


pseudopodia are always blunt. The reason for this attenuation 

of pseudopodia lacks explanation however. It is not simply 

a question of pH, for Amoebae can appear in flourishing cultures 

at pHs as low as 4 (Taylor, 12, p. 139) and at least as high 

as 7-6. Further, if the pH was ordinarily an important factor 

in determining the form of these organisms, the type ' A ' 

Amoebae would only be obtainable from cultures at the most 

suitable pH, and when the types ' E ' and ' C ' occurred at all in 

the same cultures, they would be localized in areas which, by 

reason of the metabolism of other organisms, were beyond the 

range of favourable pHs. There may actually be a small 

variation in pH over the bottom of a standing culture, but it 

is so small as to make no difference whatever to the variety of 

forms that may be yielded from different areas of it. 

The colloidal nature of protoplasm is an accepted principle ; 

and in active attenuating forms the change of phase from 

the fluid internal sol to the gelated condition of the surface 

layers must take place very rapidly. Schaeffer points out 

(9, p. 90) that this is accompanied by dispersion in a high degree 

of the internal phase of the latter, and depends upon the 

amount of water in the protoplasm. It seems probable, therefore, 

that transference of a type ' A ' Amoeba from culture 

medium to distilled water is followed by imbibition and 

diffusion of water through an ever-increasing surface to increase 

the fluidity of the protoplasm. This, combined with the loss 

of adhesion and absence of ions essential for normal contractility, 

e. g. calcium ions (Pantin, 8) expresses itself in great 

attenuation. 

3. Of the Eelationship between the types 'A', 

' E ', and ' C '.—Their mobility leaves little doubt that the 

type ' A ' Amoebae are the most healthy forms in culture 

media. They are more likely to reproduce by fission and to 

produce encysted young than either of the types ' E ' or ' C ' 

therefore, and the comparative unhealthiness of the latter may 

be indicated by the approximation of the type ' A ' Amoebae 

to their form, after long residence in distilled water. The 

inadaptability of the types ' E ' and ' C ' to changes in the


environment, their occurrence in small numbers in flourishing 

cultures, and their abundance in stale or overcrowded ones, 

points to the same conclusion. Cultures that are deliberately 

stocked with these forms fail altogether, and it is for these 

reasons that it seems probable that the bulk of those Amoebae 

which fail to enter on the cycle of encystment and which were 

mentioned at the commencement of this paper, belong to the 

types ' E ' and ' C '. 

SUMMARY. 

1. The behaviour of the adult Amoeba proteus has 

been studied in their aquarium culture media, in distilled 

water, and in dilute pure solutions of various acids and bases 

of known and graded pHs. 

2. Amoebae belonging to three physiological types are 

described from the cultures. The majority are large, active, 

digitate forms, which adhere closely to the substratum, and are 

grey in colour when seen in transmitted light. On transference 

to pure media they become attenuated, floating forms, to 

which the name type ' A ' Amoebae has here been applied. 

The remainder are darker in appearance and less adherent in 

the culture media. They belong to two types, which from their 

behaviour in pure media have been separated as type ' R.' and 

type ' 0 ' Amoebae. 

3. The association between the floating form and the capacity 

for adhering to the substratum is stressed. 

4. The problems of adhesion, of attenuation in pseudopodia, 

and of the relationship between the types of Amoebae are 

discussed. 

I wish to express my gratitude to Dr. Monica Taylor, S.N.D., 

without whose splendid material this investigation could not 

have been pursued, and my sincere thanks for their kind 

criticism and advice to Professor J. Graham Kerr, Dr. G. S. 

Carter, and Mr. C. P. A. Pantin. 

March 1926.


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3. Gruber, Karl.—" Uber eigenartige Korperformen von Amoeba proteus 

", 'Arch. Protistenkunde', Bd. 23. Jena, 1911. 

4. Jennings, H. S.—' Contributions to the study of the behaviour of the 

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5. Brooker Klugh.—" The Plunger Pipette : A new instrument for 

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6. Mast, S. 0.—" Mechanics of locomotion in Amoeba ", ' Proe. Nat. 

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Some Observations on the Behaviour of Amoeba proteus.

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