532 



THE AMERICAN NA T URALIST- [Vol. XLI 



ZOOLOGY 



Oogenesis in Insects. — It is a much debated question whether 

 the sex or germ cells are set apart at the outset of embryonic 

 development or arise later by modification of certain of the somatic 

 or body cells. The continuation of Marshall's studies on the anatomy 

 and embrj'ology of the wasp Polistes pallipes ^ treats of the early 

 history of the cellular elements of the ovary. The author finds that 

 in the embryos and very early larvie, each undifferentiated ovary is a 

 sync;yi:ium with a number of nuclei similar in structure. In the course 

 of development oocytes, primitive nurse-cells, and follicular epithelial 

 cells are developed from the undifferentiated cells of the distal end of 

 the egg tube. In a similar study of a Phryganid ^ he found that the 

 first differentiation had taken place in a fairly old larva. At this 

 stage the cells may be either "1st, undifferentiated or, 2d, passing 

 through the first stages in the development which is to result in the 

 further differentiation of oocytes or nurse-cells. Cells of the first 

 group may either remain unchanged and become the epithelial cells 

 or they may pass through the same stages as tliose of group two." 

 Thus ilarshall believes that the sex cells arise late and have a common 

 origin w-ith certain other cells in the ovary. 



These results agree essentially with those of the earlier workers, 

 notably Korschelt, 'SG, on the history of the giM-m cells of inse.-rs. btit 

 are in'sharp contrast to the results of Ilcyiiioiis Lcc-iillon '0(1 01, 

 and many other recent workers \\ ho r,,iiirii.l tliai ;lir -mii cfll- ;iiv iu 

 origin perfectlv distinct from the lolliciilar cpitlu'liuin. 



^ ^ * W. A. IUlky. 



Parthenogenesis of Bacillus rossii. -The theory that each body cell 

 contained both male and female constituents, and that the egg cell in 

 becoming mature gave off its male elements in the second polar body 

 has aiso^'been much discusMMl. Tliis idea was su[)ported by finding 

 that the second polar body was not given off froTu certain eggs which 



