244 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



the sacculations of the female portion disappear. Immediately 

 anterior to the bursa enters the slender duct of a spherical 

 vesicle, the spermatheca (receptaculum seminis, Swammerdam's 

 vesicle, copulatory pouch of Guiart). The spermatheca (spth.) 

 lies ventral to the pericardium, to the floor of which it is 

 attached by connective tissue. Its wall is thin and the matted 

 contents are of a purple or pinkish colour. The duct is so 

 slender that unless care be taken it will be cut through in 

 dissection and the vesicle left attached to the floor of the 

 pericardium. 



Anterior to the bursa seminalis there is no distinction 

 externally between male and female portions of the duct, which 

 n arrows and becomes more muscular as it nears the external 

 opening. Muscle bands encircle it, and also connect it with 

 the sub-pallium, in which it becomes embedded. 



The common genital aperture (c. gen. ap.) is situated on 

 the right side of the body at the junction of the sub-pallium 

 and the neck, at the level of the anterior insertion of the 

 parapodium. There is here an abrupt change from imple- 

 mented to pigmented skin. 



Through the genital aperture pass (a) the sperms of the 

 animal that produces them (this animal will be referred to as A), 

 (b) the egg cordon of A, and (c) sperms from another individual 

 B, for the fertilisation of the eggs produced by A. 



From the genital orifice a shallow ciliated groove (sem. gr.) 

 runs forward somewhat diagonally to the penis, situated at the 

 base of the right anterior tentacle. This groove, the seminal 

 or spermatic groove, is unpigmented. Its lateral walls are 

 formed by projections of the body wall, the left fold being 

 rounded in section, the right sharper and frilled. By approxi- 

 mation of the two folds, a tube is formed along which the 

 sperms pass from the common genital aperture to the penis. 



The penis (Fig. 19, pn.) is completely retractile within its 

 sheath, but is not invaginable. It is a pedal structure. The 



