293 



suggestion does serve to correlate and throw some light on a nunaber 

 of points : viz., the orthodromic character of amitosis and the cyclical 

 character of mitosis; the occurrence of amitosis both in regions of 

 rapid embryonic growth and in specialized cells involved in intense 

 activities along special lines; its occurrence in starving tissues or 

 organisms before disintegration ; and finally its frequent association 

 with degeneration. The occurrence of amitosis in nuclei imbedded in 

 the yolk of meroblastic eggs may seem at first glance to oppose this 

 hypothesis. It is at least posible, however, that such nuclei are unable 

 because of the small amount of cytoplasm about them to take up 

 sufficient nutrition to maintain equilibrium. Whether the cases of so- 

 called amitosis observed under experimental conditions are due to 

 conditions of the same nature as those which bring about amitosis in 

 normal tissues is at present uncertain. 



III. Amitosis and the Hypothesis of Chromosome 

 Individuality. 



The hypothesis of the "individuality of the chi'omosomes" is at 

 present receiving more attention than any other cytological hypothesis. 

 Strictly speaking the usual designation of the hypothesis is a mis- 

 nomer. The term chromosome connotes a purely morphological con- 

 ception and the chromosome as a morphological individual is certainly 

 short-lived. This hypothesis, however, is in reality not a hypothesis 

 of the individuality of the chromosome but as I understand it a hypo- 

 thesis of the continuity of the specific organization of individual 

 chromosomes, and it is as such that it must be examined. We may 

 first consider the basis on which the hypothesis rests. 



In the first place the possible or probable nature of the processes 

 involved in the maintainance of individuality or continuity is rarely 

 considered. It is at least open to question whether the hypothesis 

 does not in the final analysis involve assumptions of metaphysical 

 character. At any rate the belief in the continuity of specific organi- 

 zation seems to me to present far greater difficulties than the belief 

 that the chromosomes are what they appear to be, viz., periodical 

 phenomena accompanying periodically recurring conditions. There are 

 at least analogies for this belief, such as the constancy under like con- 

 ditions of crystal and fluid forms and various other physical phenomena, 

 but science does not at present afford a basis for a belief in „chromo- 

 some individuality" such as the hypothesis demands. If it is a fact 

 it is unique among known phenomena. 



Methods of cytological investigation at present in vogue can never 



