444 



PHYLUM MOLLUSCA 











not at the same time. Moreover, their paths are different, 

 for the portion of the duct down which the ova travel is 

 much plaited, while the path which the spermatozoa 

 follow is a less prominent groove, incompletely separated 

 from the other. Both paths are glandular, and the glands 

 on the male side are often called prostatic. 



(e) At the base of this comm.on duct, a distinct vas 

 deferens diverges to the left and leads into a muscular penis, 

 which can be protruded at the single genital aperture and 



retracted by a special 

 muscle. Before the vas 

 deferens enters the 

 penis, a long process 

 or ftagelhim is given off. 

 It is like the lash of 

 a whip, and is as long 

 as the common duct. 

 Its secretion is used in 

 forming a sperm-packet 

 or spermatophore of a 

 large number of sper- 

 matozoa, which are com- 

 pacted together at the 

 time of sexual union 

 partly in the flagellum, 

 partly in the penis. The 

 spermatophore is trans- 

 ferred by the penis into 



¥iG. 2ss.Sn3.i\ {Helix pomatia) Xa^ymg the genital aperture of 

 its eggs. — After Meisenheimer. another snail. 



( f) Continued from 

 the oviducal side of the common duct, there is a 

 separate ciliated oviduct. This has a short course, 

 and ends in the common genital aperture. Before it 

 reaches this, however, the oviduct is associated with two 

 structures. The first of these is a long process, as long as 

 the common duct beside which it runs, in appearance 

 suggesting the flagellum, but expanding at its free end into 

 a globular sac — the receptaculum seminis or spermatheca. 

 In Helix aspersa a long slender diverticulum is given off 

 from the duct of the receptaculum. This is also occasion- 







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