l6o THE GERM-CELLS 



breaks up into smaller and smaller ^i^raniiles {Lunibricus, JlToIgida, 

 Pliolciis, some myriapods, Antcdou), which scatter throu^^h the cyto- 

 plasm and are believed by many observers ( Halbiani, Mertens, \Vill, 

 Calkins, Crampton, Nemec), following the earlier views of Allen 

 Thomson, to become directly converted into deutoplasm-spheres 

 (Fig. 80). Other observers (Van Hambeke, Foot, Stiihlman, and 

 others) adopt the original view of Siebold, that the fragments of 

 the yolk-nucleus are absorbed or converted into protoplasmic 

 elements and thus only indirectly contribute to the yolk. In still 

 other cases {^c.g. the "vitelline body" of Lii)iiilus) the yolk-nucleus 

 does not fragment, but seems to serve as a centre about which new 

 deutoplasmic material is formed. A review of the general subject 

 shows that we are justified only in the somewhat vague conclusion 

 that the yolk-nucleus is probably involved in some manner in the 

 general cytoplasmic growth ; and that the facts strongly suggest, 

 though they hardly yet prove, that at least some forms of yolk-nuclei 

 are products of the nuclear activity and form a connecting link 

 between that activity and the constructive processes of the cyto- 

 plasm. That the yolk-nuclei have no very definite morphological 

 value, and that they are not necessary to growth, seems to be shown 

 by Henneguy's observation, that in the eggs of vertebrates it is in 

 some forms invariably present, in others only rarely, and in still 

 others is quite wanting ('96, p. 162). If this be the case, we must 

 conclude that the yolk-nucleus consists of material that contributes to 

 the constructive process, but is not necessarily localized in a definite 

 body. As to its exact role we are, as Henneguy has said, reduced 

 to mere hypotheses.^ The facts indicate that this material is a prod- 

 uct of the nuclear activity, and that it may in some cases contribute 

 directly to formed elements of the cytoplasm. It is probable, how- 

 ever, that beyond this the yolk-nucleus may su])ply materials, perhaps 

 ferments, that play a more subtle part in the constructive process, 

 and of whose physiological significance we are quite ignorant. The 

 whole subject seems a most interesting and important one for further 

 study of the actions of the cell in constructive metabolism, and it is to 

 be hoped that further research will place the facts in a clearer light. 



2. Origin of tJic Spermatozoon 



(a) General. — The relation of the various parts of the sperma- 

 tozoon to the structures of the spermatid is one of the most 

 interesting questions in cytology, since it is here that we must 

 look for a basis of interpretation of the part played by the sperma- 



1 '96, p. 170. 



