RELATION BETWEEN AMITOSIS AND MITOSIS. 1 75 



But even in this period mitoses occasionally occur, their rela- 

 tive frequency differing in different chains, proglottids and 

 regions. These differences may be due to local differences in 

 nutrition ; doubtless different chains and often different proglot- 

 tids, receive different amounts of nutritive material, and in those 

 best nourished, some of the nuclei may attain equilibrium occa- 

 sionally. The fact that mitoses were more frequently observed 

 near the lateral borders than in the middle of the proglottid may 

 be due to similar differences in condition. Near the lateral border 

 the proliferating regions — chiefly testes — are less numerous 

 than in the middle regions and the absorptive surface is relatively 

 greater hence more nutritive material may be available for each, 

 and conditions permitting mitosis may be more frequently attained 

 than elsewhere. 



Moreover, mitoses in the developing testes and ovaries seem 

 to occur more frequently in the later stages during the last divi- 

 sion preceding the growth period, than in earlier stages. It is 

 probable that in these stages the stimulus to growth is not as 

 great as in earlier stages and some of the nuclei attain a condition 

 of equilibrium. 



It is by no means certain that the peculiar process of fragmen- 

 tation of the spermatocyte-nuclei (Child, 'oyd) is to be regarded 

 as due to the same conditions as other cases of amitosis. On the 

 other hand, there can be little doubt that the conditions which, 

 according to the hypothesis, favor amitosis are present in the 

 testes. The development of each testis involves the formation 

 of a relatively enormous amount of nuclear and cytoplasmic 

 material and each prologottid contains hundreds of testes. Failure 

 to attain equilibrium might be expected here if anywhere. In- 

 deed the frequent degeneration of masses of cells in the testes 

 (Child, 'oyb) seems to indicate very clearly that insufficiency of 

 nutrition and failure to attain equilibrium exist, especially as this 

 degeneration is much more frequent in some chains and proglot- 

 tids than in others. Apparently some cells are forced so far 

 from equilibrium that they can no longer exist. It has been 

 noted (Child, 'oyd) that such degeneration of cells was not ob- 

 served in stages from the beginning of the growth-period to the 

 spermatid. It is not improbable that cells which once enter upon 



