54 Edmund B. Wilson. 



division of the lobe into two. Even if the lobe be cut in two 

 after its removal, the fragments likewise pass through alternating 

 periods of activity and rest closely similar to those of the whole 

 lobe, as is shown in Figs. 99, 100 (the original lobe was somewhat 

 larger than in the other cases shown). This proves that the 

 power of a rhythmic change of form involving the temporary 

 formation of lobe-like structures, is not a property of the lobe as 

 a whole, or of the lower polar area, but is inherent in the sub- 

 stance of which it is composed. It would be interesting to com- 

 pare in this respect the behavior of the isolated lobe, or fragment 

 of a lobe, with fragments from other regions of the fertilized egg. 

 Such fragments would probably also exhibit rhythmic changes, but 

 I hazard the conjecture that their activity would be found to 

 differ in some definite way from that of the lobe-fragments. 



The phenomena above described, which deserve further careful 

 study, are of interest both cytologically and embryologically. 

 First, since both the nuclei and the centrosomes are absent, it 

 follows with great probability that even in the cleavage of a 

 whole egg the constriction of the cell that leads to the formation 

 of the polar lobe takes place wholly independently of either these 

 structures or the astral rays, which suggests the possibility that 

 the same may be true of the constrictions that lead to complete 

 cell-division. Second, since the rhythm in the formation of the 

 polar lobes in the enucleated fragment coincides with that shown 

 in the division of the nucleated fragment, it is clear that as far 

 as the lobe-formation is concerned the cytoplasmic division rhythm 

 is quite independent of that of either the centrosome or the chro- 

 mosomes. This fact may be placed behind the one earlier de- 

 termined by Boveri ('97), Zlegler ('98) and myself ('01), that 

 the rhythmic activities of the chromosomes and of the cen- 

 trosomes are likewise independent, or at least separable. But 

 beyond this it Is remarkable that the periodic activity in the non- 

 nucleated fragment is not merely of a rhythmic character, but 

 changes its character at the time of the fourth cleavage when in 

 the normal development the material of the polar lobe no longer 

 forms a merely temporary structure, but is permanently cut off 

 by a cell-division. We here catch a glimpse, as It were, of a 



