Savory - Arachnida 1977

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276 IV. DE ARACHNOLOGIA Thomisidae, which he describes as the ideal laboratory spiders, capable of living in anything. Bonnet's great work on Dolomedes is a model of its kind, unsurpassed in extent and fullness of detail, while in his study of the life-history ofNephila, the same author has succeeded in hastening the development of the females and retarding that of the males, so that members of the same cocoon reached maturity simultaneously, a striking modification of natural events. In addition to this it is a fact not sufficiently recognized that the Arachnida in general and perhaps spiders in particular provide very suitable subjects for the study of animal behaviour. They are essentially animals of the small-brained type, richly endowed by heredity with instinctive modes of behaviour but without the power to learn that is possessed by big-brained creatures. It is often unnecessary to postulate the existence of a thinking or conscious mind in interpreting their actions, so that Arachnida may successfully be used by mechanistic biologists as examples of automata or organic machines. It is probably for this reason that they are so ready to live an undisturbed life in our observation cages. On occasions in the past, experiments on insect behaviour have yielded untrustworthy results because the insect did not exhibit its natural reactions when in captivity, and Acari, Solifugae and, sometimes, Opiliones have been found to give untrustworthy results due to behavioural changes when in captivity. But these are on the whole exceptional difficulties. The circumstances of captivity seldom disturb the placid and amenable arachnid, its mechanical responses are called forth and its behaviour can be measured and often predicted, as if one were working with a galvanometer or a spectroscope. An important feature of the recording of observations made of an active animal is due to the physical limitations of the human observer. The forgetting of a detail may be avoided by immediate note-taking, but it may well happen that by the time the note is made the animal has proceeded to the next stage of its operations, and this may be completed before the hurried observer looks at it again. This can be avoided by those who possess the necessary equipment by making an immediate report of everything seen into a tape-recorder, from which it can be recovered and repeated as often as necessary. REARING Bonnet's work on Nephila, mentioned above, as well as that of other competent technicians, affords proof that the life history of an Arachnid can be accurately determined by raising specimens from birth to maturity. The eggs of spiders, harvestmen and false scorpions usually 32. PRACTICAL ARACHNOLOGY 277 hatch in normal laboratory conditions without difficulty. They run opposing risks from desiccation, which effectively kills them, and damp, which encourages the growth of equally fatal moulds. The general advice to "Keep ova not too warm and not too wet" can only be successfully followed after trial and possible error. Where conditions are controllable a temperature of 20°C and a relative humidity of near 40% are usually near the optima. After their escapE from the egg membrane young spiders must be kept apart in separate vessels; other young arachnids are seldom equally cannibalistic. They need food, and as a rule will accept most of the small invertebrates that normally accompany them in lEaf litter. In many laboratories the culture of Drosophila is a continuing operation and provides a readily available source of nourishment. It must be remembered that Arachnida on the whole feed occasionally and digest slowly; also that they usually cease to feed just before ecdysis. Those who deal with exotica, such as scorpions and Solifugae, can replace Drosophila by locusts, which are as easily cultured. The chief features to be determined are the number of ecdyses that take place between birth and maturity, the length of the intervals between successive moultings, and hence the total life span. These differ from order to order and even from family to family. An unexpected difficulty is encountered in the rearing ofharvestmen, and may, perhaps turn up with other orders. Harvestmen possess the advantage that they do not need to be given living prey, but they counter this by dying an early death after the third or fourth ecdysis. Klee has given both explanation and cure. The cause is the constancy of humidity in the cages, which prevents complete hardening of the new cuticle after moulting. The conditions of nature are more closely followed if the lid of the cage is opened daily to allow the humidity to fall from 100%) to about 40%. Rearing in the laboratory and the consequent production of a complete timetable for the life of a species is one of promising lines of straightforward arachnology at the present time. The cast-off exoskeleton deserves the closest scrutiny, as one by one they display the stages of growth. The admirable work of P. D. Gabbutt on false scorpions and of .Max V achon on spiders of the genus Coelotes are examples of this. The knowledge they have provided often makes it possible to determine the instar of a given specimen from details of its leg joints or its setae.
278 IV. DE ARACHNOLOGIA EXCURSUS A Laboratory Course in Arachnology There are probably few, if any, university courses in practical zoology in which Arachnida can hope to occupy as much as the ten periods for which the work outlined below is designed. The full course may, howenr, be used as a basis from which selections can be made, while a few specialists or others working privately may wish to follow it completely and to supplement it. In recognition of this, the work has been divided into two parts, general and special. GE!':ERAL couRsE. This consists chiefly of examining and drawing the demonstration specimens provided, and the preparation of microscope slides of entire specimens of some of the smaller Arachnida. The part occupies five periods of about two hours each. 1. (i) Limulus, dorsal view: Cephalothorax; abdomen; telson; compound eyes; simple eyes. (ii) Ventral view: Cephalothoracic limbs 1-6, gnathobases on 2-6; digging process on last leg; genital operculum; abdominal limbs 1-5, with book-gills; anus, telson. (iii) Casts offossil forms, such as Eurypterus and Prestwichia. (iv) Scorpion, dorsal view: Chelicerae; pedipalpi; carapace; median eyes; lateral eyes; mesosomatic segments 1-7; metasomatic segments 1-5; telson. (v) Ventral view: Chelicerae; pedipalpi; legs 1-4 with gnathobases on 1 and 2; genital operculum; pectines; four pairs of stigmata; telson. 2. Araneae A moderate-sized spider, preserved in 70'/c 1 alcohol or freshly killed by dropping into boiling water, is gently boiled in dilute (10%) potassium hydroxide. The viscera are thus entirely dissolved and the exoskeleton which remains is rapidly upgraded to absolute alcohol, cleared and mounted in balsam under a large cover-slip. Under 1-in. objective draw the following. (i) Dorsal view: Chelicerae; pedipalpi; legs 1-4; cephalothorax; abdomen. (ii) Ventral view: Chelicerae; pedipalpi with maxillary gnathobase; labium; sternum; legs; epigyne; book-lungs; spinnerets. (iii) From a mature male spider the pedipalpi are detached. One is dehydrated and mounted on its side in its normal state; the other is 32. PRACTICAL ARACHNOLOGY 279 boiled in potash until the organ has expanded, when it is dehydrated and mounted. 3. Opiliones A harvestman with its legs cut through the femora near the body is boiled in potash and mounted whole. (i) Dorsal view: Chelicerae; pedipalpi; eyes; orifices of odiferous glands; cephalothorax and abdomen broadly joined; vitta. (ii) The characteristic penis of the male or the ovipositor of the female can easily be extracted from the abdomen after an incision has been made slightly to one side of the middle line. These parts are then mounted. (iii) After this, the legs of one side of the same specimen are removed. This makes it possible to pull the other group of coxae in the opposite direction, exposing the normally hidden vestigial sternum, and, if the genital plate is pulled back, the first abdominal sternite. (iv) Permanent mounts of a chelicera, of a pedipalp and of a single tarsus are also well worth making. 4. Pseudoscorpiones These should be studied by the method described by J. C. Chamberlin. The chelicerae and pal pi and the legs of the first and fourth pairs are removed from the body, dehydrated, cleared and mounted. The body is gently boiled in potash, washed, stained with magenta or fuchsin, cleared and mounted. All the characteristic features are well displayed by this method. 5. Acari Cheese mites, Tyrophagus, and red-spider mites, Tetranychus, are readily obtainable for mounting. A drawing is made from the ventral aspect, showing: thorax and abdomen broadly fused; chelicerae; pedipalpi; legs; genital orifice; anus. Various species of mites are easily found by bringing a boxful of drifted leaves and similar vegetable debris into the laboratory and turning it out on to a sheet of paper. The mites that crawl out are straightway drowned in spirit. Quite satisfactory preparations may often be made by merely allowing their bodies to dry and covering them with a drop of balsam and a cover-slip. But crude methods like this are not necessarily to be encouraged. SPECIAL COURSE. Owing to the small size of most of the Arachnida, and the difficulty of obtaining the largest species in Britain, this course is of necessity based on the spider. Spiders, however, justify this choice since they are the most highly specialized order. This course also occupies five periods.
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Arachnida THEODORE SAVORY 2nd editi
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Contents Preface Acknowledgements .
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MAIAE CARISSIMAE UXORI SECUNDAE LIB
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1 The Phylum Arthropoda The phylum
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6 I PROLEGOMENA The comparison impl
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10 I. PROLEGOME);A one time so rare
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14 I. PROLEGOMENA The most striking
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18 U. DE ARACHNIDIS it, move to a f
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3. MORPHOLOGY: EXTERNAL APPEARANCE
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26 II. DE ARACHNIDIS 3. MORPHOLOGY;
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30 II. DE ARACHNIDIS yet arachnolog
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34 II. DE ARACHNlDIS curved. It oft
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38 II. DE ARACHNIDIS 4. PHYSIOLOGY:
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42 II. DE ARACHNIDIS fibres run upw
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46 II. DE ARACH~IDIS As a rule the
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50 11. DE ARACHNIDIS (iii) Inversio
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54 II. DE ARACHNIDIS FIG. 21. Newly
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58 II. DE ARACHNIDIS Pseudoscorpion
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62 11. DE ARACHNIDIS of the exoskel
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66 II. DE ARACHNIDIS Sometimes the
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70 II. DE ARACHNIDIS using a scanni
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74 II. DE ARACHNIDIS constitutes th
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78 II. DE ARACHNIDIS think of Arach
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82 II. DE ARACH::-.;IDIS declined t
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86 II. DE ARACHNIDIS .Man is the on
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90 11. DE ARACHNIDIS Autecology con
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11. PHYLOGENY: EVOLUTION 95 11 Phyl
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98 II. DE ARACHNIDIS An obvious ass
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102 II. DE ARACHNIDIS start preserv
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106 II. DE ARACHNIDIS Here are thre
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110 11. DE ARACHNIDIS Araneae, and
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13 The Order Scorpiones [Scorpionid
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118 Ill. PROLES ARACHNES 13. THE OR
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122 III. PROLES ARACHNES CLASSIFICA
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126 III. PROLES ARACHNES 14. THE OR
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130 Ill. PROLES ARACHXES The lowly
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134 Ill. PROLES ARACHNES to be seen
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16. THE ORDER SCHIZOMIDA 139 16 The
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142 Ill. PROLES ARACHKES power, an
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146 III. PROLES ARACHNES DISTRIBUTI
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150 III. PROLES ARACHNES chelicerae
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154 Ill. PROLES ARACHNES FIG. 53. S
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158 Ill. PROLES ARACHNES (vi) Lobed
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162 III. PROLES ARACHNES is found i
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166 III. PROLES ARACHNES 4 (3) Chel
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20. THE ORDER TRIGONOTARBI 171 20 T
Page 93 and 94: 174 Ill. PROLES ARACHNES 22 The Ord
Page 95 and 96: 178 III. PROLES ARACHNES The family
Page 97 and 98: 182 III. PROLES ARACHNES are above
Page 99 and 100: 186 Ill. PROLES ARACHNES opisthosom
Page 101 and 102: 190 Ill. PROLES ARACHNES Sub-order
Page 103 and 104: 194 III. PROLES ARACIINES 25. THE O
Page 105 and 106: 26 The Order Acari 26. THE ORDER AC
Page 107 and 108: 202 III. PROLES ARACHNES Tetrastigm
Page 109 and 110: 206 Ill. PROLES ARACHNES 26. THE'.
Page 111 and 112: 210 Ill. PROLES ARACHNES ( 1) Notos
Page 113 and 114: 214 Ill. PROLES ARACHNES The sevent
Page 115 and 116: 218 Ill. PROLES ARACHNES family, Ho
Page 117 and 118: 222 Ill. PROLES ARACHNES posterior
Page 119 and 120: 226 III. PROLES ARACHNES 28. THE OR
Page 121 and 122: 230 Ill. PROLES ARACHNES From the f
Page 123 and 124: 234 Ill. PROLES ARACHNES 29. THE OR
Page 125 and 126: 238 Ill. PROLES ARACHNES The chelic
Page 127 and 128: 242 IlL PROLES ARACHNES 29. THE ORD
Page 129 and 130: 30 Economic Arachnology The Arachni
Page 131 and 132: 250 IV. DE ARACHNOLOGIA Although th
Page 133 and 134: ··~~- -..... 254 IV. DE ARACHNOLO
Page 135 and 136: 31 Historical Arachnology The histo
Page 137 and 138: 262 IV. DE ARACHNOLOGIA spiders qui
Page 139 and 140: 266 IV. DE ARACHNOLOGIA little was
Page 141 and 142: 32 Practical Arachnology The practi
Page 143: 274 IV. DE ARACHNOLOGIA hard. In th
Page 147 and 148: 33 Chemical Arachnology In the stud
Page 149 and 150: 286 IV. DE ARACHNOLOGIA not very pl
Page 151 and 152: 290 IV. DE ARACHNOLOGIA seventeenth
Page 153 and 154: 294 IV. DE ARACHNOLOGIA A new aspec
Page 155 and 156: 298 IV. DE ARACHNOLOGIA For more th
Page 157 and 158: 36 The Spider's Web The webs that s
Page 159 and 160: 306 V. HETEROGRAPHIA a number ofver
Page 161 and 162: 310 V. HETEROGRAPHIA dramatically p
Page 163 and 164: 314 ( i) ( ii) ( iii) (iv) (v) V. H
Page 165 and 166: 318 V. HETEROGRAPHIA this may be ad
Page 167 and 168: 322 V. HETEROGRAPHlA .1\Jenge in 18
Page 169 and 170: 326 VI. EPILEGO:VIENA Vellard, J.,
Page 171 and 172: i 330 Vl. EPILEGO~iENA Lamoral, B.
Page 173 and 174: 334 VI. EPILEGOMENA Ill. Bibliograp
Page 175 and 176: INDEX ANIMALIUM 339 Index Animalium
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Savory - Arachnida 1977

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