252 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



spermatogenesis of other invertebrates) to form four 

 spermatids. Disc-shaped masses of spermatids are thus 

 produced, the thickness of which is equal to about one- 

 fourth the diameter of the face (fig. 65). In each mass 

 there is a central cavity containing the remains of the 

 blastophore, a small quantity of a slightly fibrous 

 coagulum being present. Each spermatid undergoes no 

 further division, but is gradually transformed into a 

 spermatozoon. An early stage of this transformation is 

 seen in fig. 64. The nucleus is an oval compact body at 

 one end of which is a small conical mass of protoplasm, by 

 which the spermatid is attached to the blastophore. This 

 becomes the apical body or acrosome of the spermatozoon. 

 At the opposite end of the nucleus there is a clear sub- 

 stance from which the " middle piece " of the sperma- 

 tozoon is apparently largely derived, and following this 

 is the rest of the protoplasm, which is being drawn out to 

 form the tail of the sperm. When shed into the sea the 

 ripe spermatozoa soon become free from the blastophore 

 and move b} T means of the tail, which appears to be a 

 somewhat stiff filament capable of comparatively limited 

 movements (hg. 66). A ripe spermatozoon is about '058 

 nini. long, it has a curiously shaped head "04 mm. long, 

 and a long slender tail ('054 mm. long). The nucleus forms 

 the greater part of the head of the sperm. At one end is 

 the apical body forming a cap slightly sub-divided by a 

 median groove. It is by means of this apical cap that the 

 sperm is later attached to the egg with which it is about to 

 unite. At the other end of the nucleus is the middle 

 piece which is apparently notched behind to receive the 

 basal part of the tail. Ripe sperms may usually be 

 obtained about the end of February or the beginning of March. 

 The genital products, instead of floating freely in the 

 cceloniic fluid, often accumulate in the space between the 



