384 COMPARATIVE ANATOMY. 



In the other hermaphrodite forms the two ducts are, as a rule, 

 separated earlier, and the common canal undergoes merely unim- 

 portant modifications. The separate canals are modified in various 

 ways, the vas deferens is very long in most of the Opisthobranchial.i, 

 and is consequently arranged in a number of coils. It is frequently 

 united with a superiorly attached, and occasionally wider, gland, 

 before it reaches the copulatory organ. The oviduct is not so long", 

 and is but seldom much widened out. At the end, however, of the 

 female efferent apparatus there are a number of accessory organs. 

 The two sets of efferent ducts either open into a common space 

 (generative cloaca), which is generally placed on the right side of, 

 and towards the anterior region of the body, or the two canals open 

 into a shallow depression, or they may open separately from one 

 another, and on the surface of the body. 



§ 296. 



The appendages of the generative apparatus may be 

 divided into those which belong to the male, and those which belong* 

 to the female systems. The receptaculum seminis is one of the most 

 important of the female organs. It is a rounded or pear-shaped 

 vesicle, inserted by a hollow stalk into the vagina, and receives the 

 semen at the time of copulation (Fig. 204, Its.) Sometimes there 

 are two of these appendages (Pleurobranchus), which maybe placed 

 at some distance from the vagina, and on the narrower oviduct 

 (Doris). In the Pteropoda and Opisthobranchiata the vagina is pro- 

 vided with a wide diverticulum, the glandular walls of which are set 

 in folds, and which functions as a uterus. A special glandular organ, 

 which resembles in arrangement the albuminiparous gland, opens 

 into it. When this organ is absent, the wall of the uterus appears 

 to take on its function. Lastly, we must mention the copulatory 

 pouch of the Pteropoda, which appears to be a diverticulum of the 

 vagina, and receives the penis during copulation (Hyalea). 



The male apparatus, also, is provided with organs of this kind, 

 which, in their simplest form, are widened parts or enseal structures 

 for the collection of the sperm. That elongation of the vas deferens, 

 which we have already mentioned, is physiologically an organ of this 

 kind. Similar arrangements are found in both the Gastropoda and 

 the Pteropoda. The glandular organs attached to the vas deferens 

 are also organs of this series ; they are ordinarily known as prostatic 

 glands. 



Lastly, the male apparatus is connected with a copulatory 

 organ, which is either the modified and eversible end of the seminal 

 duct, which when not in use projects into the coelom, or it is a special 

 organ, which has no direct connection with the vas deferens, and 

 which, when not in use, forms a retracted tube. The organ is either 

 connected with the generative orifice, as in many Nudibranchs, 

 or is separated from it. In the Tectibranchiata (Aplysia, Bulla, 

 Bullrea, etc.), the penis opens at a great distance from the common 



