STUDIES ON GERM CELLS 413 



two; and nucleus c is apparently undergoing a second amitotic 

 division before the first division is actually completed — the 

 result would probably have been a row of four nuclei. As 

 recorded by Child ('07), Patterson ('08), Maximow ('08), Wie- 

 man ('10b) and others, amitosis here likewise occurs in rapidly 

 dividing nuclei and is probably due to some physiological con- 

 dition. 



A type of amitosis differing from that just described was 

 discovered in eggs that had been subjected to the action of 

 centrifugal force. The three nuclei shown in figure 57 are from 

 vitellophags of an egg of Leptinotarsa decemlineata which was 

 centrifuged for sixteen hours after deposition and was then fixed 

 immediately. The chromatin in nuclei a and h forms rather 

 condensed clumps in the center of the nucleus and the nuclear 

 membrane appears to force its way through the center of this 

 clump thus bringing about the formation of two daughter nuclei. 

 This rtiembrane cannot be a cell wall since vitellophags do not 

 possess cell walls, and this appearance cannot be due to poor 

 fixation because other nuclei in this egg were perfectly preserved. 

 This sort of division must therefore be a normal process or else 

 due to some unknown influence of the centrifugal force. Various 

 authors have contended that there are within the nuclear mem- 

 brane all the elements necessary for an equal division of chromatin. 

 This view is supported by the discovery of part or all of the 

 mitotic figure within the nuclear membrane in certain cells, 

 e.g., during the maturation division of Canthocamptus (Hegner, 

 '08). The case just described and figured in this paper contrib- 

 utes to the support of this hypothesis. 



C. The growth of the oocytes and development of testicular cysts 

 in Chrysomelid beetles 



The investigations on Chrysomelid beetles described in the 

 succeeding pages were undertaken for the following purposes: 

 (1) To study the differentiation of the nurse cells and oocytes 

 from the oogonia; (2) to determine the origin of the pole-disc 

 granules; (3) to discover, if possible, stages in the cycle of the 



