136 George Lefevre 



smaller and containing fewer chromosomes, has been cut trans- 

 versely in the middle. It is difficult to determine how figures 

 like these have arisen, but since the number of chromosomes is 

 greatly increased, nuclear division has undoubtedly occurred re- 

 peatedly without accompanying cleavage of the cytoplasm. Their 

 origin could be accounted for by supposing that, after several 

 nuclear divisions have taken place, probably through multipolar 

 mitosis but without cleavage of the cytoplasm, all of the chromo- 

 somes have been gathered into a single large nucleus which, at the 

 next mitosis, is converted into a bipolar figure by the appearance 

 of only two asters in connection with it. 



c Monasters 



Mention should be made of another common type of abnormal 

 forms, the striking single radiate systems or monasters which have 

 been described by previous observers, notably Hertwig ('96), 

 Morgan ('00) and Wilson ('01). 



In Thalassema the monasters are only found in unsegmented 

 eggs, the closely set rays forming a beautiful corona around the 

 nucleus. I have never observed the monaster to resolve itself into a 

 bipolar figure, nor to produce a segmentation, but the same alter- 

 nating phases of activity, involving the rhythmic disappearance 

 and reappearance of the rays and successive division of the chromo- 

 somes, as have been described by Wilson ('01, p. 546) for Toxop- 

 neustes, also occur in the monasters of Thalassema. These periodic 

 changes are undoubtedly comparable, as Wilson maintains, with 

 the progressive transformations of the nucleus in dividing eggs. 

 I have frequently been able to observe in the livingegg the periodic 

 changes in the rays of the monasters, although they cannot be 

 seen very distinctly. Sections show that the chromosomes usually 

 lie at the center of the aster in a clear, hyaline area, from the border 

 of which the rays diverge (Fig. 60). In a few cases, some of the 

 chromosomes are found scattered amongthe rays, although this con- 

 dition does not seem to be the common one, as it is in Toxopneustes, 

 and in none of the monasters in my material have I found such 

 figures as Wilson has described, where the center is formed by a 

 spongy centrosome from which the rays radiate (l.c.y Figs. 40, 41). 



