XII 



PHYLUM MOLLUSCA 



749 





FIG. 641. Follicles of the ovotestis of the Gastropoda. A 

 of Helix hortensis (Pulmonata) : B, of the Eolidae . 

 a. a, ova ; b, masses of sperms ; c. common efferent duct. 

 (From Gegenbaur.) 



may be simple or may be incompletely divided longitudinally into 

 two parts. In the Pulmonata the first part (" hermaphrodite duct " 

 proper) is simple, and 

 serves for the pas- A 



sage both of ova and 

 sperms : the middle 

 part is incompletely 

 divided internally into 

 two passages, one serv- 

 ing as oviduct, the 

 other as sperm-duct. 

 In the distal part 

 oviduct and sperm- 

 duct are completely 

 separate. Where the 

 sperm-duct enters the 

 penis, there is given 



off a long, slender, tapering diverticulurn, the flagellum (flag.\ 

 in which the sperms are made up into elongated masses or 



spe rmato^)hores. 



Development. The 

 limpets (Patella) are ex- 

 ceptional in laying the 

 eggs one by one and un- 

 f e r t i 1 i s ed im pregnation 

 taking place in the water 

 after they have been dis- 

 charged. In almost all 

 the Gastropoda fertilisa- 

 tion is internal, and the 

 eggs are laid in great 

 masses, embedded in jelly, 

 each egg having its own 

 hyaline envelope. Very 

 often the mass of spawn 

 consisting of the jelly-like 

 substance, with the eggs 

 embedded in it, attains 

 a relatively considerable 

 size. In form it varies 

 greatly : frequently it is in 

 the shape of long strings 

 which are cylindrical or 

 band-like: sometimes 

 several such strings are 

 twisted together into a cord. Sometimes the spawn is fixed to 

 sea- weed or other objects ; sometimes it is unattached, and may 

 VOL. i 3 B 



FIG. r,4-2. Forms of egg-cases in Gastropoda. A and 

 D, Pyrula or Busycon ; B, Conns ; t', 

 Voluta musica; E, Ampullaria. (From 



the L'ambriiint Satv.ral History.) 



