116 SEXUAL ORGANS. 



placed in double rows on a ribbon, the circumvolutions of which 

 with margins overlapping, formed the cylindrical shape. 



Gastropoda. Prosobranchiates, etc. The sexes are distinct in 

 the prosobranchiates ; the organs are, however, very simple and 

 so alike in structure, that frequently the sex of the gland can 

 only be determined by microscopical examination. Usually a 

 germ-secreting gland is imbedded in the liver, from which an 

 efferent duct opens at the right side into the mantle-cavity. In 

 most cases the males may be readily distinguished by the large 

 penis, which is placed at the right side of the head behind the 

 eyes. In Patella, Haliotis, Hipponj^x and Trochus there is no 

 copulatory organ. Their genital gland opens in the neighborhood 

 of the anus. Latreille has proposed the name Agama for gas- 

 tropod mollusks without copulatory organs ; the others are 

 distinguished as Exophallia by Morch. The shell in the female 

 is generally more inflated than in the male. 



Female Organs (xvi, 89). The ovary discharges into a much 

 looped oviduct, and the latter dilates into a gut-like uterus — the 

 last portion of which on account of its muscular wall may be 

 regarded as a vagina. There is sometimes at the comrnencement 

 of the uterus, or at its connection with the vagina, a seminal 

 pouch, but other appendicular organs are seldom present. 



The last portion of the uterus or even the whole of it, and the 

 vagina lie in the respiratory cavity, to the left by the side of the 

 rectvim and nearest to the abdominal wall. The sexual opening- 

 is accordingly found to the left of the anus, but usually far 

 behind it. Sometimes the uterus is split through its entire 

 length and its folds formed by the longitudinal and transverse 

 plaits, consequently lie freely exposed in the respiratory cavity. 

 Lacaze-Duthiers has so described it in Yermetus. 



There is scarcely anything to be said in regard to the eggs of 

 the prosobranchiates, generally. Where their development can 

 be seen, a distinct germinal vesicle and germinative dot are 

 present ; but when they leave the ovarium the yolk granules 

 are present in such numbers as to conceal this structure. 

 In the oviduct, or quite above the uterus, the eggs come into 

 contact with the zoosperms, which are occasionally retained at 

 this point in a spermatheca. Further down in the uterus fertil- 

 ization could no longer be effected as they here become enclosed 

 in a tough albumen, and finally are covered, usually many 

 together with a firm capsule. These egg-capsules, in their various 

 shapes, will be described presently. 



Male Organs (xvi, 91). These are simpler than those of the 

 female ;. the efferent canal is not divided into so many succeeding 

 portions, but instead a copulatory organ (penis) is placed 

 anteriorly, the structural peculiarities of which present much 

 that is noteworthy. 



