428 PTEROPODA. 



gus near the middle of the neck. There are eight large and two 

 smaller ganglionic masses closely aggregated in this situation, and 

 from these sources all the nerves of the body are given off. 



(469.) From the large dimensions of the nervous centres we may 

 be prepared to expect senses of correspondent perfection of structure. 

 We have already mentioned the sensitive tentacula protruded from 

 the hood-like covers that protect the oral apparatus ; but, in addi- 

 tion to these, organs of vision are provided, apparently of a very 

 complete character. These eyes are two in number, and are placed 

 on the back of the neck. Each eye has the form of a somewhat 

 bent cylinder, having its two extremities rounded off. The anterior 

 end of the cylinder is the transparent cornea ; and when the eye is 

 removed from the body of the animal, and examined under the 

 microscope by transmitted light, sundry parts may be detected in 

 its interior, sufficient, indeed, to indicate the existence of a choroid 

 membrane, a vitreous humour, and a distinct lens, occupying the 

 ordinary positions of these parts of the visual apparatus. 



(470.) The generative system of Clio resembles in all essential 

 particulars that of the most highly organized Gasteropoda ; and, as 

 in them, is composed of a complete set of male organs as well as of 

 ovigerous viscera. According to the views which Cuvier was led to 

 entertain from the dissection of a single specimen, he supposed that 

 the ovary (fig. 200, ri) gave off a slender oviduct (o) terminating 

 in a thick glandular canal, the testicle (k) ; which, beginning by a 

 csecal prolongation, and gradually diminishing in diameter until it 

 became attenuated into a slender vas deferens (p), ultimately 

 emptied itself into a small round sac (q) situated in one side of the 

 neck where it communicated with the exterior. Close to the sac 

 (q) the illustrious French anatomist pointed out another vesicle 

 (r), which he compared to the bladder (spermatheca) of Gasteropod 

 Mollusks. The more complete researches of Professor Eschricht 

 have, however, rendered considerable modifications of the above 

 description requisite ; inasmuch as that gentleman has succeeded 

 not only in detecting a testis quite distinct from the oviferous canal, 

 but also a very complete intromittent apparatus. The testis, in 

 fact, in a fresh specimen is so large as to occupy a great portion of 

 the visceral cavity ; and, no doubt, in the individual examined by 

 Cuvier, which had been kept in spirits of wine, it formed a large 

 portion of the mass (Jig. 200, i), which he thought to be entirely 

 made up of the liver. The duct from this testis communicates with 

 the receptacle (</), so that the glandular canal (k) must be regarded 



