38 MR. T. H. HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 
The Mantle is very well developed ; a peculiar thickened and ciliated band crosses 
it transversely, and seems to be the homologue of the subspiral ciliated band in 
Firolo'ides (d). 
Contractile aSuc.— T his resembles the corresponding organ in Firoloides it lies 
between the rectum and the heart, and opens into the bottom of the chamber of the 
mantle by a well-defined oval aperture, figs. 3 and 4 c. 
Generative Organs.— The ovary or testis is an elongated mass corresponding to the 
liver, and occupying the inner and right half of the visceral mass, fig. ?>t. ^ 
The Ovary consists entirely of a mass of ova in course of development, with their 
characteristic germinal vesicle and spot. The oviduct commences at its anterior 
larger extremity ; it is very wide and passes forwards, forming many convolutions, 
and terminates in the mantle-cavity by the side of the anus. ^ 
The Testis contains a mass of small cells and spermatozoa in various stages of deve- 
lopment. 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. ^ i • 
There is a kind of penis attached to the right side of the neck of the ammal just 
above the foot (^, fig. 1) : it is composed of two portions arising from a common 
base. The anterior and inner is like a three-pointed leaf; a csecal ciliated canal luns 
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 Firoloides, cannot be misunderstood, and the posi- 
tion of the organ in Atlanta corresponds with that in Firoloides, 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 Firoloides, 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 afterwards unite into one. They are 
connected with the suboesophageal or pedal ganglia {y), two large oval masses fiom 
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. 
* In Carinaria a similar commissural nerve, between the cephalic and the parieto-splanchnic system of 
ganglia, has been shown to exist by Milne-Edwards {loc. cit.), but I could find none in Firoloides. 
