326 MM. Koren and Danielssen on some 
ventral surfaces, where they form leaf-like processes. In its 
walls there are many large round cells, the contents of which 
consist of fine dark granules (hepatic cells). Towards the 
hinder part of the body the stomach contracts considerably, 
as it passes into a short intestine, which opens into the 
branchial cavity. The whole of the inner surface of the ali¬ 
mentary canal is furnished with ciliated epithelium. 
Circulatory Apparatus. 
In the posterior end of the body there is between the 
mantle and the intestine (rectum) a space in which the 
heart is situated. Into its hinder margin opens the common 
stem of two vessels, which come from the still more posteri¬ 
orly situated branchiae; and from the anterior end issues a 
single vessel, which passes into the mantle above the posterior 
termination of the genital gland, and at once begins to ramify. 
Along the middle line of the belly, just above the course of 
the mantle-furrow, runs a vessel which we have been unable 
to trace. 
Generative Organs. 
Along the dorsal surface of the animal, in the same direction 
as the keel, and between the latter and the stomach, lies the 
hermaphrodite gland, which is lobate, consists of a number of 
acini, and has in the middle a tolerably wide efferent duct. 
When this has come a little way out of the gland, it divides 
into oviduct and vas deferens. Into the oviduct open the 
efferent ducts of the albumen-gland, which is three-lobed and 
oblong. As regards the vas deferens , we have reason to think 
that it divides, but cannot state any tiling with certainty upon 
this point ; for we have seen the connexion between the vas 
deferens and the penis-sheath only on one side, without being 
able to observe any division. On each side of the vestibulum 
there opens in its lateral margin a penis-sheath, which is 
extraordinarily muscular, and is clothed inside with cylinder- 
epithelium. Each of these sheaths encloses a compressed 
horny sheath, which is open along one margin, and at the 
posterior extremity beset with numerous small appendages; 
within this sheath, again, lies the true style (penis), which is 
likewise compressed, and terminates in a sharp point. The 
vestibulum is tolerably wide, with firm walls clothed with 
ciliated epithelium ; and into it, besides the two penis-sheaths 
already described, there opens a small oblong vesicle with a 
short efferent duct ( receptaculum seminis ), as well as two 
looped mucus-glands with a common duct. The little oblong 
