224 BULLETIN OF THE 



new attitudes towards its fellow.* Alterations within the yolk are not 

 easily observable. The light spots grow somewhat less distinct, but 

 further than this nothing can be seen. 



In returning to the study of the normal course of development of 

 hardened eggs, I begin at the point where its consideration was left for 

 the purpose of presenting the abnormal conditions shown by the presence 

 of a number of spermatozoa in a single yolk. 



In the eggs of most animals the pronuclei, after attaining their maxi- 

 mum size and coming into close contact, suifer a mingling of their sub- 

 stances by the disappearance of the limiting envelopes (membranes) that 

 for a time separated them. This union becomes so complete that authors 

 speak of the resultant structure as a single body, — a unit, which has 

 been called the nucleus of the first segmentation sphere. In the case of 

 Limax, we find that this unit structure is sought with very questionable 

 success. The first cleavage nucleus^ does 7iot have a morphological existence. 

 I seek an explanation of the fact by assuming that the acceleration at 

 this stage of the ontogeny is so great that the division of this promised 

 structure is begun before it has an actual independent existence. To 

 say the least, the first evidences of the coming separation of the yolk 

 have already made their appearance, while there are still two distinctly 

 separate pronuclei. I refer in these evidences to the new stellar shapes 

 which arise in the protoplasm of the yolk in the vicinity of the two pro- 

 nuclei, and which are destined to become the amphiaster of the first 

 cleavage sphere. Undoubtedly, the two new centres of activity which 

 now come into existence are only a part of a continuous process of trans- 

 formation which neither begins nor ends with them, — a process which 

 slowly obliterated the great spiral archiaster, and which will in turn 

 cause them to disappear; but it is equally certain that they belong 

 strictly to the phenomena of the first segmentation. In their beginnings, 

 these new centres exert an influence which, though not far reaching, is 

 vigorous and aggressive. All observations hitherto agree in making the 

 visible changes connected with these two centres synchronous in their 

 appearance ; and this may well be true for the majority of cases. It-, 

 however, is not universally so, for in several of my preparations (Figs. 52, 

 73, 79, 80) very satisfactory evidence is afforded that one of the new 

 centres may exert an influence of considerable extent before its mate 

 has produced the slightest visible sign of its existence. 



Usually these new stellar figures centre at points on, or very near, the 



* The mutual flattening of the products of segmentation, and other interesting 

 phenomena of the same period, cannot be considered in the present paper. 



I 



