50 C. 0. Whìtman 



they arrise de novo; is only a rather immodest way of saying that 

 their orig'iu remains to be determiued. That there is some genetic re- 

 lation between these cells and tlie nucleus of the germogen appears 

 to me much more probable than any contradictory hypotbesis. The 

 points of analogy between the residual nucleus and the central nucleus 

 of the vermiform embryo make it somewhat probable that the first cell, 

 or cells that arise in the germogen are formed at the expense of both 

 the nucleus and the protoplasm. The origin of subsequent generations 

 of cells would then present no difficult3^ even if the nucleus henceforth 

 became inactive, as in the case of the nucleus of the axial cell. The 

 passivity of the nucleus would only render the parallel between the 

 germogen and the axial cell still more complete. Whatever be the role 

 of this nucleus , the germogen agrees with the axial cell in beiug the 

 generatrix of germ-cells , and in containing a nucleus that sooner or 

 later becomes entirely inactive. The comparison is not at all impaired 

 by the interesting diiference , that the development of the germ-cells 

 takes place in one case within , in the other outside, the parent cell. 



The similarity between the germogen and the axial cell with re- 

 spect to the formation of germ-cells called forth the following remark 

 from Van Beneden : «Ces germes se formeut donc dans les cellules 

 germigènes à peu près comme les germes des embryons vermiformes 

 dans le corps de la cellule endodermique.« I think this statement may 

 be fully correct , although the opinion on which it was based , that the 

 germ-cells in both cases arise, not from pre-existing cells. but as entirely 

 new and independent formations , is certainly incorrect in one case and 

 probably so in both. 



It remains to consider to what extent the peripheral cells of the 

 Infusorigen are comparable with the ectoderm of the vermiform embryo. 

 That the peripheral cells ])ursue the path of ectoderma] development 

 for only a short distance and tlien abandon it altogether in becoming 

 free germ-cells . is certainly a very interesting difference between the 

 two layers ; but this fact raises no insuperable objection to their morph- 

 ological equivalence. It is not incompatible with our present kuowl- 

 edge of functioual differentiation, to suppose that a layer of cells which 

 has once played the role of an ectoderm , might , under conditions that 

 render an ectoderm useless , revert to that kind of work to which all 

 others are subservient, namely, reproduction. Such a reversion would 

 not imply any fundamental change in the character of the cells; it 

 would be simply a resuraption of a function that had fallen into 

 abeyance. as a result of those specializing conditions which bring about 



