CLIO BOEEALIS. 



557 



from the circumstance of the nerves being of a pale-red colour. The 

 ganglia form a ring placed around the oesophagus 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. 



(1495.) 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 addition to 

 these, organs of vision are provided, apparently of a very complete cha- 

 racter. 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. 



(1496.) The generative system of Clio resembles in all essential 

 particulars that of the 



most highly organized Fig. 279. 



Gasteropoda, and, as in 

 them, is composed of a 

 complete set of male 

 organs as well as of ovi- 

 gerous viscera. Accord- 

 ing to the views which 

 Cuvier was led to enter- 

 tain from the dissection 

 of a single specimen, he 

 supposed that the ovary 

 (fig. 279, n) gave off a 

 slender oviduct (o) ter- 

 minating in a thick glan- 

 dular canal, the testicle 

 (&), which, beginning 

 by a csecal prolongation, 

 and gradually diminish- 

 ing 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 



Viscera of Clio borealis: mm, the heart, giving off a 

 large vessel ; t, oesophagus ; v, intestine ; w, salivary 

 glands ; n, ovary ; o, oviduct ; k, testicle ; p, its excretory 

 canal ; q, bladder-like organ. 



