MUSEUM OF COMPARATIVE ZOOLOGY. 469 



egg, AuERBACH ('74, pp. 210-217) says that they continue their mo- 

 tion until they become, to a considerable extent, mutually flattened. 

 The line of contact is very fine, and the failure of the nuclei to melt 

 tooether at once is due to that condition of the surface of the two nu- 

 clear drops known to physicists as superficial tension, and not to the 

 existence of a veritable nuclear membrane. The flattened pair of nuclei 

 soon commence a rotary motion around an axis perpendicular to the 

 long axis of the egg, which continues till the plane of separation, which 

 originally was perpendicular to the long axis, comes to lie parallel with 

 it. The rotation, like the migration of the nuclei, is passive, i. e. is 

 efl"ected by the contractility of the protoplasm. Toward the end of this 

 rotary motion the nuclei become more flattened, and the nucleoli be- 

 come, one after the other, gradually paler and somewhat larger, and 

 then suddenly their substance scatters, forming a cloud, which almost 

 immediately vanishes. After this the line of separation suddenly dis- 

 appears along its whole extent, and the two nuclei are one. If it were 

 a layer of protoplasm or a membrane which separated the nuclei, it 

 could not disappear throughout its entire length at the same instant. 

 The single nucleus by elongation now assumes a rhombic or broad- 

 spindle form. 



When he comes to an interpretation of the meaning of this melting 

 together of two nuclear structures, Auerbach believes that it is to be un- 

 derstood as a sort of conjugation (pp. 248, 249), — a necessary introduc- 

 tion to the process of successive nuclear increase, which is soon to follow. 

 Hence it is a kind of nuclear reproduction. Just as for the reproduction 

 of individual organisms a copulation of two individuals is so often indis- 

 pensable, so for unicellular organisms is that of two cells. Every conju- 

 gation has manifestly for its end the improvement (by a process of 

 intermingling) of individual peculiarities, — the mutual complementing 

 of deficiencies. A difl'erence in the two uniting elements, so common 

 elsewhere, is not wanting here. The difference in the place of origin of 

 the polar nuclei — the one at the smaller pole where the spermatozoa 

 penetrated, the other at the opposite pole — will influence the quality 

 of the nuclear material and induce one-sided faults in the composition of 

 each. To correct this is the object of the migration and confluence of 

 the primitive nuclei. But if these were simply to meet and coalesce, 

 then, owing to the inability of the thick nuclear fluids immediately to 

 intermingle, the whole process would be futile, since with the first 

 segmentation each half of the nuclear mass would be relegated to the 

 half of the yolk in which it arose. This is obviated by the rotation of 



