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R. T. Young 
expression of tlie degeneration of mitosis in this group. Tliis hypothesis 
adniits however of certain alternative liypotheses which shonld be men- 
tioned here. 
It has beeil suggested by various aiitliors that mitosis is periodic, of 
short diiration, and hence rarely seen. This was found to be the case in 
Pennaria and Clava by Beckwith (1909), where mitosis was absent 
except between 4 and 6 A. M. Har>lvx (1913 p. 225) however in her work 
Oll Taenia teniaejormis found that “Neither the character of cell-division 
nor the appai’ent frequency of cell-division is influenced by the time of 
the year, the time of the day, the ainount of food material, or the use of 
Chloroform” (upon the host). 
That periodicity inay explain the usual infrequence of mitosis in most 
cestode tissues is not impossible, especially in view of the observation 
by Child (1910 p. 113) of one worin in which “almost every nucleus (was) 
in mitotic division”. Such an explanation however fails totally to account 
for the skein degeneration, evidence of which is presented in this and 
my previous paper (1913), and accounts of which have been given by 
other observers. 
If my hypothesis be correct that the secondary spermatocyte nuclei 
arise from fragments of degenerating skeins, it will bring this process in 
cestodes in line with clu-omidial niiclear formation in Protozoa, wliich has 
been recorded by so many observers. That mitosis in cestodes is giviug 
place to a simpler type of cell division, is not impossible, in view of the 
degenerate condition of these worms in other respects. 
CüNKLiN (1917) has shown how various amitotic simulacra may be 
induced artificially in Crepidula plana, and uses his observations to refute 
the evidence of amitosis, which has been accumulating in recent years. 
While his work shows clearly how difficult of positive determination are 
amitotic appearances, and how guarded one must be in his Statements 
regarding them, I nevertheless believe that he generalizes too widely when 
he says, “If nuclear and cell divisions ever take place by amitosis in nor- 
mally developing sex cells and embryonic cells it would deal a fatal blow 
to that (the cln-omosome) theory” (1. c., p. 412—413). While the role of 
the cln-omosome in heredity may be universal in Metazoa and Metaphyta 
it certainly is not so in Protozoa and Protophyta; and if inheritance can 
function without chroniosonies in any of the latter groups, the assumption 
by the chromosome of the inheritance function in either the fornier or the 
latter groups must have occured secondarüy in their evolution. It ueed 
not surprise us then if certain of these groups, such as the exceedingly 
degenerate cestodes, should, as the result of such degeneracy, lose the 
