134 George Lejevre 



state, however, whether the next cleavage behaves like the second 

 maturation division or not, but it would be of interest to know if 

 the dyads reappear at that time, as might be expected. 



7 Abnormal Mitoses 



It is not my intention to describe in detail the endless variety 

 of abnormalities of mitosis that have been encountered in the 

 study of the parthenogenetic eggs of Thalassema. Most of the 

 unusual conditions which I have found are quite similar to those 

 which have been described by other observers, especially by R. 

 Hertwig ('96), Morgan ('96, '99, '00), and Wilson ('01), in the 

 unfertilized eggs of echinoderms after treatment with salt solutions 

 and other agents. It may be well, however, to refer briefly to the 

 more characteristic abnormal forms. 



a Multipolar Mitoses 



Of these, the formation of polyasters, with resulting multipolar 

 mitoses, was perhaps of the most frequent occurrence and was ob- 

 served at all stages of development from the first cleavage onward. 

 It has already been stated that the two cleavage asters, when 

 the parthenogenetic eggs develop without abnormalities, appear 

 simultaneously on the nuclear membrane, and give rise to the 

 usual dicentric figure. When three or more asters appear, instead 

 of two, they also seem to arise in situ, lying close to the nuclear 

 membrane and at quite a distance from each other. I have 

 never observed a doubling of the centrosomes in these cases of 

 multipolar mitosis, or the least indication of division of the asters. 

 Fig. 53 shows a typical case; the egg nucleus, which is here rather 

 larger than usual, is accompanied by four small asters, showing 

 central bodies, and the membrane is giving way in front of three 

 of them. As the spindles form, the nuclear area is usually drawn 

 out at the points where the asters lie, as seen in one of the cells of 

 Fig. 54, and with the dissolution of the membrane, forms like 

 these give rise to multipolar spindles. Such eggs may divide at 

 once into a corresponding number of blastomeres, as I have 

 frequently observed living eggs in which triasters and tetrasters 



