GROWTH AND DIFFERENTIATION OF THE GERM-CELLS ijl 



piece ; while in Helix or the elasmobranch it is transformed into a 

 long filament traversing a cytoplasmic " middle-piece " which forms 

 a considerable part of the flagellum. The term middle-piece has thus 

 become highly ambiguous and should only be employed, if at all, as 

 a convenient descriptive term which has no definite morphological 

 meaning. 



A very striking fact in the origin of the spermatozoon is the promi- 

 nent part played by the " archoplasm," i.e. substance in the form 

 of idiozome or Nebenkern derived from the mitotic figure. Both the 

 source and the fate of this material seem, however, to vary in differ- 

 ent cases, the acrosome now arising from the Nebenkern (insects), 

 now from the idiozome (salamander), the envelope of the flagellum 

 being formed in some cases from the Nebenkern (insects), in others 

 from unmodified cytoplasm (salamander, snail), while the idiozome 

 may form the acrosome (salamander, mammal) or degenerate without 

 apparent use (snail). We find here, I think, additional reason for 

 regarding "archoplasm" not as a distinct and permanent form of 

 protoplasm, but only as a phase in the general metabolic transfor- 

 mation of the cell-substance, which may or may not persist and play a 

 definite morphological ivie in the cell according to circumstances. 

 The close relation of this substance to the motor phenomena of the 

 cell cannot, however, be overlooked.^ 



The outgrowth of the axial filament from the centrosome is a highly 

 interesting fact, whether we compare it with the analogous phenomena 

 in plants (p. 172) or with the facts observed in ordinary ciliated cells. 

 In the latter case (Fig. 17), as has long been known, each cilium is 

 attached to a small, highly refracting body known as the " basal 

 knob " lying near the cell-periphery. These bodies stain intensely 

 in iron haematoxylin, and it has been recently suggested by Henneguy 

 ('98) and Lenhossek ('98) that they are of the same nature as centro- 

 somes. The truth of this surmise must be tested by further study ; 

 but it seems highly probable that they are at least analogous to the 

 spermatid-centrosome. Ishikawa ('99) has clearly shown that in the 

 formation of the swarm-spores of Noctiluca the flagellum grows out 

 from that end of the cell at which the centrosome lies, its substance 

 apparently arising from the central spindle, while the centrosome lies 

 at its base. A very interesting fact discovered by Moore ('95) in 

 elasmobranchs, and confirmed by Meves ('97, 5) and Henneguy ('98) 

 in the insects, is a more or less abortive attempt to form a flagellum 

 by the spermatocytes, i.e. one or two generations before the sper- 

 matozoon. In the insects (Fig. 166) Henneguy has found the cilia 

 actually attached to the centrosomes of the mitotic figure, thus remov- 

 ing every doubt as to their nature.^ 



1 Cf. 323. ^ Cf. Paulmier on giant spermatozoa, p. 165. 



