Studies ill Cnistaeeau Speriiiatogeiiesis. 403 



of bead or middle-piece are present projections or streamers wliieli 

 are entirely missing in the S. anacantlia (Text Figs. 8-12). If these 

 projections have their origin in the region of the neck the s})erma- 

 tozoon belongs to the S. ancanthina deracantha, represented by the 

 Galatheidse and Pagiiridjp, whereas if they come from the head 

 region it is classified as S, cephalacantha, represented by the 

 Brachyura, Dromiida? and Oxystomata (Text Figs. 8-12). In the 

 latter forms the tail capsule is more or less drawn into and sur- 

 rounded by the head region which gives the spermatozoon a con- 

 tracted appearance and causes it to approach more nearly a spherical 

 shape. According to Koltzoif's classification, the spermatozoa of 

 Astacus, the Loricata and the Thallassemidea are placed in a separate 

 group, the S. contracta, characterized by a shortening and broaden- 

 ing of the tail capsule. I^o very sharp line can, however, be drawn 

 between these forms and the Galatheidse and the PagTiridffi, the 

 dimensions of the tail capsule varying within comparatively wide 

 limits. 



In those Decapods which have been carefully studied the tail cap- 

 sule contains a narrow tube or vesicle within which is to be found 

 the centrosome and its derivatives. The proximal centrosome lies 

 anteriorly in the region of the processes, while a distal, elongated and 

 otherwise modified centrosome lies behind it extending into the tube, 

 (Text Figs. 8, 9, 10, 12.) A comparison with the flagellate type 

 leads to the conclusion that the nucleus may be regarded as the head, 

 the region of the processes as the middle-piece, the capsule as the 

 tail, while the modified distal centrosome may correspond to the 

 axial filament. The space between the inner tube and the outer 

 wall of the capsule is believed by Koltzoff to be occupied by an 

 explosive substance. 



The homologies of the Decapod spermatozoon have only recently 

 been satisfactorily elucidated. Auerbach (1895) interpreted the 

 jiarts of the spermatozoon much as has been outlined above, but did not 

 w^ork out the details. As late as 190-t Labbe described the capsule 

 as anterior in position to the nucleus and processes and investing 

 the acrosome. He believed it to be present only in the immature 

 spermatozoon and that as a final stage of development the nucleus 



