192 1 ] N. ANNAXDAtK & 11 B. S. Skavell ; Vivipara. 233 



(iSgij p. 665), appears to consider it to be an ejaculatory duct, 

 in which view Simroth (1896-1907, note to fig 9, pi. xliii) concurs. 

 Baudelot (1863, p. 217), on the other, hand seems to consider that 

 it is of the nature of a prostate gland, and describes the internal 

 surface as consisting of a series of transverse lamellae, running 

 parallel to each other. In V. bengalensis, this region of the duct is 

 surrounded by a layer of circular connective tissue fibres and the 

 lining mucous membrane is thrown into folds as described by 

 Baudelot, though these are narrower and more numerous than he 

 figures them. A transverse section shows that these folds 

 are supported by a connective tissue lamella, on each side of 

 which is a layer of cubical epithelium. The whole organ is glan- 

 dular in character and is in mj" opinion a ' prostate ' gland. The 

 terminal portion of the male duct is comparatively narrow. It 

 passes up the right tentacle and opens by a small orifice at its 

 extreme tip. In this part of its course the duct-wall is thick 

 and muscular, and constitutes an ejaculatory duct. 



According to Smith (1881, p. 221) the right tentacle of the 

 male Vivipara vivipara is merely the sheath of a true penis, 

 ■'which, at the time of copulation, protrudes through it." As 

 regards this statement he appears to be at variance with other 

 authors. Simroth (1896-1907, p. 617) states that the short 'penis' 

 can be coiled up in a pouch of skin at the outer side of the 

 tentacle, and Baudelot (1863, p. 218, pi. v, fig. 14) shows this 

 condition very clearly. It is this coiled up portion of the tentacle 

 which is the 'penis,' and no portion of the genital duct is pro- 

 truded through it during the act of copulation, for, as Baudelot points 

 out, the terminal portion of the duct, which I have considered 

 to be an ejaculatory duct, is intimately connected with the skin of 

 the tentacle and could not possibly be everted. In this respect 

 Vivipara vivipara and V. bengaleiisis appear to be identical. In 

 this latter species the terminal portion of the o» genital duct is 

 closely bound to the skin of the tentacle bj' connective tissue. 

 I have not been able to observe the act of copulation , but the 

 structure of the right tentacle in this species shows that here also 

 it is the tentacle itself which is the intromittent organ. 



The seminal fluid contains two quite distinct forms of sperma- 

 tozoa. The first form, which appears to be that of the mature func- 

 tional spermatozoon, consists of an elongate spiral head, with 6-7 

 turns in the spiral and of a refractile appearance ; behind this is a 

 single long flagellum. The second form is usually described as 

 * worm-shaped ' ; it may be straight or spirally twisted, is much 

 stouter than the spiral kind and terminates in a tuft of numerous 

 short flagellae. From the time of their discovery these two forms of 

 spermatozoa have interested zoologists and accounts of them and 

 their mode of development have been given by V. Siebold (1836), 

 lye^^dig (1850), Baudelot (1863), Simroth {1891-1907) and others, 

 but we are still ignorant of the function of the worm-shaped type. 

 9 . The genital organs of the female Vivipara bengaleiisis 

 appear to agree exactly with those of V. vivipara. One of the best 



