THE EMBRYOLOGY OF THE HONEY BEE 21 



The nuclei of the cleavage cells, during the resting stage, are 

 circular to broad elliptical in outline. Each contains a network 

 of achromatic material bearing on it a number of small rounded 

 granules of chromatin. No nucleoli karyosomes or plasmo- 

 somes were observed. The size of the nuclei is, in a given egg, 

 quite uniform, from the beginning to the end of the period under 

 consideration, but varies considerably in different eggs, ranging 

 from 9-14 microns. 



The position of the nucleus within the cell is very variable, 

 but it can be stated that in general the nuclei during the earlier 

 Stages (I-II) occupy a position near the center of the cell body 

 (Fig. 76). As cleavage progresses, however, the nuclei evi- 

 dence a tendency to take up a position near the margin, and this 

 tendency becomes more and more marked as the cells approach 

 the periphery of the egg (Figs. 6 and ?A). 



Nachtsheim has recently (1913) published a detailed account 

 of mitosis in the cleavage cells of both the fertilized and un- 

 fertilized eggs of the honey bee. Prior to the appearance of 

 this account the writer had also studied this subject and pre- 

 pared figures 8A-F, illustrating the different phases of mitosis. 

 The writer's observations agree with those of Nachtsheim ex- 

 cept in one or two minor details. A clearly defined spireme was 

 never observed, although in the prophases (Figs. 8A and B) the 

 chromosomes are seen to be united in short strings, which in 

 many preparations, as in that from which figure 8B was drawn, 

 give the effect of a relatively small number of curved rod-shaped 

 chromosomes, and it is only by the use of the highest magnifica- 

 tion available that these resolve themselves into the minute spher- 

 oidal chromosomes of which they are composed. No special 

 effort was made to determine the number of these. It seems 

 probable that Nachtsheim is right in estimating the number as 

 thirty-two. There are certainly more than sixteen. The centro- 

 somes, 4 densely staining minute spherical bodies, are readily seen 

 at all stages. In figure 8A they have taken positions at opposite 

 sides of the nucleus preparatory to division. Soon after this the 

 nuclear membrane breaks down, usually disappearing first at the 



* Nachtsheim, following Boveri, prefers to call these the centrioles, and 

 the surrounding zone the centrosome. The latter the writer regards as 

 the attraction-sphere. 



