234 EDITH PINNEY 



The spindles of mitotic figures in normal eggs of these two 

 species differ. In Fundulus, as the chromosomes are drawn to 

 the poles, they are crowded closely together and the polar ends 

 of the spindle are constricted (figs. 1 and 2). In Ctenolabrus 

 the separating groups of chromosomes occupy a broader field, 

 approximating in area that of the equatorial plate, and therefore 

 the anaphase spindles are more uniform in diameter throughout 

 their extent than is the case in Fundulus (figs. 8 to 10). An 

 idea of the relative areas occupied by the anaphase groups of 

 chromosomes in both species may be obtained by a comparison of 

 figure 3 with figures 11 to 15. This difference in the physical 

 character of the spindles may account for the interference with 

 the normal division of the Ctenolabrus chromosomes in the Fun- 

 dulus egg. As will be seen later, in the reciprocal cross with the 

 Ctenolabrus egg, a similar disturbance during division is exceed- 

 ingly rare. Moenkhaus found that when the egg of Fundulus 

 was fertilized by the spermatozoa of Menidia, the early cleavage 

 divisions were normal; there was no lagging. He reports, how- 

 ever, the presence of only thirty-six chromosomes in Menidia, 

 and it is possible that the mechanical difficulties offered by the 

 small Fundulus spindle are not so great when this species is used 

 in crossing as they are when the sperm of Ctenolabrus is used. 



The few late telophases of the first cleavage that were found 

 exhibited no atypical features. Nothing that could be identi- 

 fied as lagging chromosomes was observed. There are two 

 features of the Fundulus egg that might prevent the recognition 

 of extra-nuclear chromatin if it did occur. These are: first, 

 numerous large yolk granules scattered throughout the cytoplasm 

 which vary greatly in their affinity for the chromatin stain, and, 

 second, the very coarsely reticular character of the cytoplasm 

 itself, the meshes of which (and this is particularly true in the 

 region of the first cleayage plane) are very similar to the chro- 

 mosomal vesicles. 



Figures 20 to 25 show what appears to be an active elimination 

 of chromosomes from the nucleus. Figure 20 presents a cell 

 in the metaphase of the second cleavage. Two normal asters 

 are united by a spindle which is bent slightly toward the first 



