﻿130 



William S. Marshall and Paul H. Dernehl, 



Dickel (14) for Apis, have described the zone of cleavage nuclei, at 

 about a similar stage, as appearing in a pyriform arrangement in 

 longitudinal section; a line connecting all the cleavage nuclei in the 

 Polistes egg never had this outline, but was in general much more 

 the shape of the egg. Kowalevsky (31) also noted the same pyri- 

 form arrangement. 



We have already noted that in the egg of Polistes all nuclei 

 divide mitotically and that the only difference between any of them 

 is in their position within the egg. Repeated mitosis adds largely 

 to the number of nuclei in each group, the zone of cleavage nuclei 

 becoming more and more clearly defined. In the earliest stages we 

 were unable to distinguish the cleavage — from the yolk — nuclei, 

 and could not with certainty determine to which group any of the 

 nuclei then present would belong. A similarity of the nuclei in the 

 egg was early noted by Cholodkowsky (13), and Dickel (14), has 

 lately called attention to this fact. In our study of Polistes we have 

 failed to find at any stage a definite arrangement of the dividing 

 nuclei either relative to each other or to the surface or the axes of 

 the egg. Such a definite arrangement has, however, been noticed 

 in the eggs of other insects. Blochmann (2) found that the nuclei 

 forming the zone divided tangentially and radially ; in this way some 

 of the newly formed nuclei remained with those of the zone, others 

 passing inside it to become yolk nuclei. Heymons (26) has described 

 the division of the cleavage nuclei, when near the periphery, as 

 parallel to the egg's surface. Schwartze (51) found that the nuclei 

 of the zone, which was concentric to the periphery of the egg, 

 divided paratangentially to the surface. Will (61) figures nuclei at 

 the periphery, and before reaching it as dividing, but not all in 

 any one definite direction, and Henking (25) found that the nuclei 

 in the eggs of Pyrrhocoris do not divide in a tangential or any other 

 definite direction. Graber (18) and Wheeler (60) both found the 

 axes of the dividing nuclei all parallel to the longitudinal axis of 

 the egg. Heymons (26) noted in Forficida a definite arrangement 

 of the spindle in the dividing cleavage nuclei. 



In the earlier stages it was noticed that all or the majority of 

 the nuclei were within the anterior half of the egg. This arrange- 

 ment is different in older stages and one showing the zone of 

 cleavage nuclei clearly defined would give a great similarity between 

 the anterior and the posterior halves of the egg, the form er half 

 containing a slightly greater number of yolk nuclei than the latter. 



