ON THE MORPHOl.OGY OF THE CEPHALOUS MOLLUSCA 163 



commences at its anterior larger extremity ; it is very wide and passes 

 forwards, forming many convolutions, and terminates in the mantle- 

 cavit)' by the side of the anus. 



The Testis contains a mass of small cells and spermatozoa in 

 various stages of development.- The vas deferens leads from its 

 anterior extremity, and before terminating in the cavity of the mantle, 

 dilates, occasionally forming thus a dark spherical vesicula seminalis, 

 s, fig. 3- 



There is a kind of penis attached to the right side of the neck of 

 the animal just above the foot (/, fig. i): it is composed of two 

 portions arising from a common base. The anterior and inner is like a 

 three-pointed leaf ; a c^cal ciliated canal runs along its centre. The 

 posterior portion is a tubular cylindrical process, with a kind of ciliated 

 cup at its extremity (fig. 5) : a conical body projects into this below. 

 The tube is nearly filled with small oval granules. The resemblance 

 between this and the penis, which has been described in Firolotdes, 

 cannot be misunderstood, and the position of the organ in Atlanta 

 corresponds with that in Firolo'ides, if we consider the left filamentous 

 process in the latter to be the metapodium. That it is so, is demon- 

 strated not only by the distribution of the metapodal arteries, but by 

 an examination of the intermediate genera above mentioned. 



Nervous System (figs. 2 and 6). — This consists of two trilobed 

 supraoesophageal ganglia (fig. 6), which correspond to those of Firo- 

 lo'ides, and give off similar nerves ; but in addition their posterior lobes 

 give off each a long nerve,^ which runs back upon the stomach, and 

 below its posterior narrowing, between this and the aorta, joins with 

 its fellow in a small ganglion (not figured by Eydoux and Souleyet) ; 

 some branches pass from this to the viscera, and two or three run in 

 the substance of the mantle to the " ciliated band," fig. 4. 



The commissural cords which unite the supraoesophageal with the 

 suboesophageal or pedal ganglia, are at first double (fig. 6), but after- 

 wards unite into one. They are connected with the subcesophageal 

 or pedal ganglia (j/), two large oval masses from which several branches 

 are given to the different parts of the foot ; and each gives off one long 

 cord which runs along the lower surface of the intestine, and probably 

 joins the ganglion upon the aorta before mentioned. 



The Eyes {i, fig. 6) resemble those of Firoloides, except that their 

 pigment is black. 



The Auditory Vesicles are spherical and about Tj-^yth of an inch in 



^ In Carinaria a similar commissural nerve, between the cephalic and the parieto-splanchnic 

 system of ganglia, has been shown to exist by Milne-Eclwards (loc. cit.), hut I could find none 

 in Firoloides. 



W 2 



