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Wm. S. Marshall, 



groups; Istj cells with nuclei similar to those of the terminal filament; 

 2nd, those with nuclei very different from this in structure, but which 

 we believe have come from nuclei similar to the first group. Of the 

 first group there is little to be said. We meet them again in all 

 the stages we study, and, in the pupa, cells with similar nuclei form 

 the epithelial layer. These undifferentiated cells show no further 

 change in nuclear structure but, increasing in number by mitosis, 

 form the follicle around the oöcyte and the thin epithelial layer of 

 the nurse cells. While the second group shows many different nuclear 

 structures the cells all pass through the same development; as yet 

 they show no indication of their future fate. 



Mitosis occurs throughout this ovary and the question at once arises, 

 do these cells, in their development from undifferentiated ones and 

 after they have reached the second group mentioned above, pass 

 through one or two divisions, or, are the dividing cells only the 

 undifferentiated ones increasing in number. This is a difficult question 

 to answer. From our study of Polistes we found that at one time 

 all nuclei within the gonad were similar in structure; as the gonad 

 grew these nuclei increased in number, dividing mitotically. The 

 same is undoubtedly true for Plahjphijlax at corresponding stages. 

 In the older larvae and pupae of Platyphylax we fall to find nearly 

 so many dividing cells as in this stage. If the cells we have just 

 been describing, those of the second group, passed through one or 

 more divisions we must have found in some of the many ovaries 

 examined, a zone containing many cells in mitosis, or eise some 

 regiouj as that of synapsis, where a number of dividing cells would 

 occur together. This we do not find, and we hold that after the 

 oöcyte or nurse- cell has started on its development from an undif- 

 ferentiated cell, it does not divide. This we did not find true for 

 the nurse cells of Polistes where a number of divisions take place. 

 In the two insects the conditions however are different. In Polistes 

 the number of nurse-cells accompaning each oöcyte is much greater, 

 as is also the number of eggs each ovarian tubule produces. In 

 Platyphylax the eggs are all laid in a very short period, but in 

 Polistes^ this period is very much longer and the eggs in the ovary 

 are continually growing. 



Ovary B. This ovary shows a considerable advance over what 

 we found in the last one and its oldest cells are much further 

 developed. If we take any section which passes longitudinally through 



