140 A. RICHARDS. 



of the usual mitotic type is shown in a research, as yet unpub- 

 lished, by Conklin, the division figures are very difficult to find. 

 One may examine section after section without seeing a single 

 case of mitosis. Although I have not made a statistical study 

 of the two cases I am of the opinion, from the examination of the 

 slides which Professor Conklin has kindly shown me, that division 

 figures are more rare in the oogonia of Planorbis than in those of 

 Moniezia. The ratio of resting cells to dividing cells is large. 

 Yet there is no evidence for the occurrence of amitosis here. 

 Another better known example is found in the oogonia of Ascaris. 

 Any one who has searched for oogonial divisions in this animal 

 knows how few cells show them in proportion to the number 

 present. 



As development progresses mitoses occur as stated up to the 

 growth period, but, it is true, not as frequently as one would 

 expect from conditions in other tissues. I do not find that the 

 figures are always as easily recognizable as are mitoses in many 

 tissues. 



That mitoses occur throughout the development of the female 

 germs cells in considerable numbers, there is not the slightest 

 doubt. The evidence for this is positive. Furthermore, they 

 always occur in the peripheral, i. e., the growing portion of the 

 anlage, a very significant fact. It requifes merely a little careful 

 search upon properly fixed and stained material to discover them. 

 Tissues fixed in King's fluid and stained with the Flemming 

 triple stain are especially favorable for finding the mitotic figures. 

 They do not occur as frequently as one would a priori expect, 

 but, in the light of the fact which will appear immediately, i. e., 

 that there is no good evidence for the occurrence of amitosis, 

 we are merely forced to readjust our ideas of the number of 

 divisions necessary to produce a tissue. The mitotic frequency 

 has not been sufficiently considered. I regard it as also highly 

 probable that periodicity of division is an important factor in 

 tissue production. 



There are to be seen here many cases of nuclei which lie close 

 beside one another with only a narrow layer of cytoplasm be- 

 tween them. There have been some few cases in which no layer 

 could be distinguished, but the character of the material is such 



