29O C. M. CHILD. 



amii<>-i- incurred and therefore constitute not negative but 

 positive e\ idence of considerable value. They do not, of course, 

 constitute a demonstration, but, as I have pointed out abo\e, 

 an actual demonstration or proof is impossible' in fixed material. 

 To my own mind, all the facts concerning which Richards and 

 I agree, together \\ith the cases which I regard as nuclear division, 

 but which Richards has failed to find, constitute a practical. 

 though not a logical demonstration of the occurrence of amitosis 

 in Moiiiczia. On p. 127 Richards asks "whether the failure to 

 find evidence of a certain process, using proper methods and 

 exercising due diligence, is not positive evidence of the lack 

 of that proces- . J ' Such a question can of course only be an- 

 swered in the affirmative, but this does not constitute a refutation 

 of my statement that Richards had presented only negative 

 evidence for the occurrence of amitosis; it is of course merely the 

 same statement in other words. And we are all aware that pos- 

 itive evidence of the absence of something must be of the strong- 

 est character before it can be regarded as refuting direct posit i\ e 

 evidence of the presence of the same thing. Richards is unable 

 to show with anything approaching certainty that mitosis is 

 the only method of cell division in the ovarian primorciium. 

 I have presented positive evidence that amitosis occurs in ad- 

 dition to mitosis, though my evidence does not amount to an 

 actual demonstration since that is impossible. 1 believe, how- 

 ever, that the evidence for the occurrence of amitosis in the 

 (\.irian primordia of Moniezia is almost if not quite as conclusive 

 as that tor its occurrence anywhere else in other species. 



II. Tin; CLEAVAGE STAGES. 



As regards the cleavage of .\foniezia, my examination of Dr. 

 kichards's slide-, enble^ me, as mentioned above, to correct 

 the error into which I fell in maintaining that "cases of mitosis 

 .iii r.irely seen after the first cleavage, but amilosis is ot frequent 

 occurrence' '< 'hild. 'ojM. Richards's O|>MT\ ations as stated 

 in his paper led me to believe that I must ha\e been in error 

 on this point and the examination of his slides removed any 

 doubt which might ha\e remained. 



There is no question but that tin- earlier cleavages beyond the 



