1^6 C. M. CHILD. 



the growth-period possess sufficient energy to obtain nutritive 

 material, notwithstanding the demands of their rivals in earlier 

 stages, but it is also possible that some of these cells are so far 

 from a condition of equilibrium that they cannot go through the 

 maturation mitoses following the growth-period. Such cells are 

 probably those in which fragmentation occurs. Certainly the 

 process of fragmentation in the spermatocytes (Child, '076) pre- 

 sents no difficulties to such an interpretation. In it most of the 

 nuclear substance disappears and a few small nuclei are formed 

 from what might almost be regarded as the debris of the original 

 nucleus. Apparently the old nucleus is no longer able to exist 

 as a physiological system and small parts of it form new systems. 

 The special form of fragmentation in these cases may be merely 

 the result of special conditions which are not present in the primi- 

 tive cells of earlier stages. 



It is evident then that these cases of fragmentation in the 

 spermatocytes can readily be interpreted in the same manner as 

 the amitoses in other stages. Whether the resulting nuclei 

 actually take part in the formation of spermatozoa is a question 

 which cannot be decided at present. 



The typical spermatocytic mitoses were observed more fre- 

 quently in testes situated in the extreme lateral regions of the 

 proglottids, fragmentation apparently being much more frequent 

 in the middle regions (Child, 'ojb). This fact likewise is prob- 

 ably to be regarded as favoring the suggestions made above. 

 As was pointed out, in the extreme lateral regions of the pro- 

 glottid the testes are not as numerous as in the middle regions 

 and the resorptive surfaces from which nutritive material may 

 reach them are relatively greater than in the middle regions. 

 It may well be that the cells in these testes attain more frequently 

 than others a condition in which mitosis is possible. 



As regards the frequency of amitosis in cleavage of the earliest 

 stages the fact that nuclear division is always far in advance of 

 cytoplasmic division, except in those blastomeres which divide 

 mitotically (Child, 'oyd) seems to indicate the existence of a 

 strong stimulus to nuclear division in the nuclei dividing amitoti- 

 cally. Apparently most of the nuclei are forced by some factor 

 to divide much more rapidly than they acquire correlations with 



