2^20 CONTINUITY OF THE GERM-PLASM AS THE [IV. 



further on, I shall mention a fact which seems to me to furnish 

 a real proof of the validity of this explanation ; and, if we 

 accept this fact for the present, it will be clear that the simple 

 explanation now offered of phenomena which are otherwise so 

 difficult to understand, would also largely support the theory of 

 the continuity of the germ-plasm. Such an explanation would, 

 above all, very clearly demonstrate the co-existence of two 

 nucleoplasms with different qualities in one and the same 

 nucleus. My theory must stand or fall with this explanation, 

 for if the latter were disproved, the continuity of the germ- 

 plasm could not be assumed in any instance, not even in the 

 simplest cases, where, as in Diptera, the germ-cells are the 

 first-formed products of embryonic development. For even in 

 these insects the ^gg possesses a specific histological character 

 which must depend upon a specifically differentiated nucleus. 

 If then two kinds of nucleoplasm are not present, we must 

 assume that in such cases the germ-plasm of the newly formed 

 germ-cells, which has passed on unchanged from the segmenta- 

 tion nucleus, is at once transformed entirely into ovogenetic 

 nucleoplasm, and must be re-transformed into germ-plasm at 

 a later period when the egg is fully mature. We could not in 

 any way understand why such a re-transformation requires the 

 expulsion of part of the nuclear substance. 



At all events, my explanation is simpler than all others, in 

 that it only assumes a single transformation of part of the 

 germ-plasm, and not the later re-transformation of ovogenetic 

 nucleoplasm into germ-plasm, which is so improbable. The 

 ovogenetic nucleoplasm must possess entirely different quali- 

 ties from the germ-plasm ; and, above all, it does not readily 

 lead to division, and thus we can better understand the fact, in 

 itself so remarkable, that egg-cells do not increase in number 

 by division, when they have assumed their specific structure, 

 and are controlled by the ovogenetic nucleoplasm. The ten- 

 dency to nuclear division, and consequently to cell-division, is 

 not produced until changes have to a certain extent taken place 

 in the mutual relation between the two kinds of nucleoplasm 

 contained in the germ-nucleus. This change is coincident with 

 the attainment of maximum size by the body of the egg-cell. 

 Strasburger, supported by his observations on Spirogyra, con- 

 cludes that the stimulus towards cell-division emanates from 



