HISTORY OF CHROMOSOMAL VESICLES IN FUNDULUS. 26l 



Conklin has developed the idea of karyomeres, or chromosomal 

 vesicles, basing it upon his observations and experiments, to 

 such a stage of completion that he can show all stages of combina- 

 tions from single vesicles on up to that of the entire complex. 

 He figures cases that very closely resemble amitosis as shown by 

 various workers, and suggests that this superficial resemblance 

 may be a source of error in some at least of the observations 

 upon which the claims of the occurrence of amitosis have been 

 made. This suggestion may be reiterated here, for it is obvious 

 that if there should be an indention between two of the vesicles 

 in the resting stage of a Fundulus nucleus, direct division would 

 be at once called to mind. 



The polarity of the cell is definitely maintained in dividing 

 Fundulus eggs. As the chromosomes pass to the poles their long 

 axes lie in the cell axis, which passes through spheres and nuclei, 

 and the vesicles are formed with this polarity. Cytoplasmic 

 division follows only slowly after nuclear division and the 

 nucleus has entered upon the phase of interkinesis by the time 

 that the cytoplasmic separation is accomplished. Also before 

 cytoplasmic separation, the centrosome divides and each half 

 traverses an arc of 90 in preparation for the next division. 

 This results in the establishment of a new cell axis at the right 

 angles to the old. Thus for a time the old and the new axes 

 exist together, the daughter nuclei themselves marking the 

 old and their divided centrosomes the new. Fig. 16 is such a 

 case, the two cells shown having arisen from the result of the 

 division of an ectodermal cell of a blastula. The line con- 

 necting the points A and B represents the axis of the parent 

 cell, while CD and EF respectively mark the axes of the daughter 

 cells. The fact that the two latter are nearly perpendicular to 

 each other is of significance when it is remembered that in the 

 next division the upper of these cells will produce the two ecto- 

 dermal cells and the lower two mesodermal. 



The polarity is recognizable in the vesicles in many cases, 

 the longer axes of the vesicles in general lying in the cell axis. 

 It is, therefore, evident that about the time of centrosomal 

 separation the polarity of the vesicles changes. Earlier oriented 

 with respect to the old sphere, they have now shifted to the newly 



