ARACHNIDA. 315 



ganglion, c, that represents all the abdominal ganglia collected 

 into one mass ; and from the posterior part of this, nerves, w, w, 

 destined to supply the parts contained in the abdomen, derive 

 their origin. The thoracic ganglia, e, e, are fusiform, and placed 

 on each side of the mass c, with which they are apparently 

 amalgamated at one extremity, while from the opposite they give 

 off the nerves appropriated to the legs. 



The ocelli or eyes of Arachnidans have been minutely investi- 

 gated by M tiller,* and seem to present a type of structure very far 

 superior to that of insects. In the Scorpion this distinguished anato- 

 mist succeeded in detecting most of the parts which enter into the 

 construction of the eye of a vertebrate animal ; and, moreover, 

 a great similarity in their arrangement. The cornea, a globular 

 lens, the aqueous and vitreous humours, the retina and choroid 

 were all found nearly in their usual relative positions ; so that the 

 sense of vision in these animals must be extremely perfect. 



(361 .) The sexual organs of the male and female Fig. 145. 



Arachnidans exhibit very great simplicity in their 

 structure. The testes, or secreting vessels of the 

 male spider, are two long cseca (Jig. 145, 6), lodg- 

 ed in the abdomen, and terminating by simple 

 orifices at the ventral surface. No external in- 

 tromittent organ is perceptible ; and it was on 

 this account that the peculiar apparatus above re- 

 ferred to, situated at the extremity of the maxil- 

 lary palpus, was so long considered as giving pas- 

 sage to the impregnating secretion. The singular 

 instrument already described ( 355), would seem, 

 indeed, to be in some manner really subservient 

 to the fecundating process ; being used most probably as an exciting 

 agent preparatory to the intercourse between the sexes. 



(362.) The ovigerous system of the female is equally devoid of 

 complication, and, like the male testes, consists of two elongated 

 membranous sacculi, in which the eggs are formed and brought 

 to maturity. The impregnation of the ova is evidently effected by 

 the simple juxta-position of the external orifices of the two sexes : 

 yet such is the ferocity of the female spider, that the accomplish- 

 ment of this is by no means without risk to her paramour; for the 

 former being far superior to the male, both in size and strength 

 (Jig. 146, A, B), would infallibly devour him, either before or after 

 * Annales des Sciences Nat. tom.xvii. 



