Il8 CM. CHILD. 



occurrence of what seemed to me to be undoubted cases of ami- 

 tosis in a number of species from different groups of the animal 

 kingdom, without attempting in most cases to determine its fre- 

 quency or significance, and added a brief consideration of the 

 physiological and theoretical significance of amitosis in general. 

 Concerning my observations in this paper Richards says (p. 31 1) 

 that my " evidence is lacking in some respects." I scarcely see 

 how other evidence than positive statements and figures can be 

 given and must suggest the desirability of more definite criticism 

 than this, for in discrediting another's observations it is no more 

 than just to present definite reasons for one's position. 



And finally : if my obsei'vations are not in accord with certain 

 current hypotheses it is not because of any preconceived opinions 

 on my part concerning those hypotheses, but simply because the 

 results of my work have forced me to believe that the hypotheses 

 are not in accord with all the facts. As regards this point, it 

 would seem that our present knowledge of regulatory phenomena 

 in organisms is sufficient to show very clearly that certain results 

 may be attained in different ways under different conditions. 

 Moreover, the periodical recurrence of specific structures in defi- 

 nite form and number is one of the most characteristic features 

 ■of the organic cycle, but we do not regard it as necessary to be- 

 lieve that those structures should persist as distinct and contin- 

 uous entities during the periods when they are not visible. To 

 speak specifically, why should we regard the chromosome prob- 

 lem as fundamentally different from the problem involved in the 

 recurrence in each generation of five fingers upon a hand, or the 

 regulatory development of a definite and characteristic number of 

 tentacles in a piece of an actinian body ? The farther we pro- 

 ceed in our physiological analysis of developmental phenomena, 

 the more evident does it become that the finger and the tentacle 

 do not persist as distinct and definite entities during all the period 

 when they are not present as visible structures. The only thing 

 which persists is the physiological capacity to react in a certain 

 way under certain conditions, and when these conditions arise the 

 characteristic structure-complex appears. 



In short, when we consider the chromosome problem from a 

 physiological instead of a purely morphological point of view, and 



