Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
40 II. DE ARACHNIDIS<br />
4. PHYSIOLOGY: INTERNAL ORGANS 41<br />
SACCULE IN<br />
LABYRINTH<br />
SOMITE SAC LABYRINTH EXIT<br />
,..,-<br />
!.('\:::_____ "'-~~~<br />
,,_,_:~::,<br />
L---- --~~------<br />
__ r,-,_ ______ _<br />
vii<br />
-----~<br />
vili<br />
----- --..r----1<br />
FIG. 14. Coxal glands. Solifugae; (vii) Theraphosomor;•hae; (viiii<br />
Lycosidae, ,\gdenidae, Thomisidae; (xi _\raneidae, Pbokidar.<br />
inside the eo m olu tccl portion and from whi,:h short exit tu bcs open to<br />
the exterior at small orifices behind the first and third coxae.<br />
In Solifugae and Palpigradi, there is an additional tube, the labyrinth<br />
sac, lined with secretory cells, between the saccule and the labyrinth.<br />
The orifice in these forms is on the pedipalpal somite.<br />
The following table shows the \'ariations which occur among the<br />
different orders of <strong>Arachnida</strong>. The most variable order is the Arancar,<br />
X<br />
5 and 6 Absent Coils in 3<br />
somite 5<br />
Amblypygi 3 !Extensive<br />
l coils to<br />
Uropygi 4 and 5 somite 6<br />
Araneae<br />
'1'heraphosomorphae 3 and 5 Large, coiled I and 3<br />
Araneae<br />
Gnaphosomorphae 3 Straight tube<br />
Palpigradi 2 Extending to Small vesicle Pal pi<br />
somite 8<br />
Solifugae 2 Extending to Coils to Pal pi<br />
somite 4 somite 6<br />
------·"~··-···-<br />
in which four types exist showing a progressive simplification, correlated<br />
with a corresponding increase in complexity of the silk glands.<br />
The Malpighian tubes are of interest because they are a parallel to<br />
the similar tubt's of Insecta but are not their homologues, for the tubes<br />
in <strong>Arachnida</strong> ha\'C a hypodermal origin, compared with the ectodermal<br />
origin in Insecta. They are the chief excretory organs of <strong>Arachnida</strong>:<br />
they branch copiously among the many mid-gut diYerticula from one or<br />
two points of origin on the posterior end of the mesenteron. Their<br />
epithelial cells absorb waste matter from the haemocoele, transform it<br />
and excrete it in the form of guanin to the hind-gut. Here it mixes with<br />
the faecal rrsiducs in the stercoral pocket until ejected, either periodically<br />
or, sometimes, at moments of shock or stress.<br />
l\Ialpighian tubes do uot enter the prosoma. In this region<br />
cells known as nt>phrocytcs absorb the products of metabolism from the<br />
blood sinuses. Other types of the hypodermic cells below the<br />
exoskeleton and the superficial and interstitial cells round and bet\\Cen<br />
the intestinal di\·erticula also play a in the absorption of f'Xcreta.<br />
The bodies or Aradmida arc \Tl'V fully provided with glands. There<br />
arc venom glands in Scorpiones and Pseudoscorpioncs, silk glands in<br />
Acari, Pseudoscorpiones and Araneac. acid glands in l~ ropygi and<br />
odoriferous glands in Opiliones, The glandular systems iuvoln:d are<br />
usually peculiar to one order, so that fuller accounts of them will be<br />
found in the appropriate chapters in Part Ill.<br />
nearly all the mO\·ements of an arachnid are movements of its<br />
and its month parts. it is not surprising that its muscles are very<br />
unequally divided hetvvcen the prosoma and the opisthosoma. \Vithin<br />
the former there is a conspicuous endosternite, a plate of chitin to which<br />
most of the muscles are attached. Typically four pairs of bands of muscle
Change language