340 ETHEL NICHOLSON BROWNE 



The main conclusions that can be drawn from these experi- 

 ments are: (1) Three layers of materials can be segregated in the 

 spermatocyte cells of Notonecta by means of the centrifuge, a 

 cap of oil drops, a clear protoplasmic layer and a layer of mito- 

 chondria. (2) The mitochondria are definite bodies which can 

 be separated from the protoplasm proper, and they are the 

 heaviest material in the cells. (3) Nonnal division figures occur 

 in spite of the redistribution of materials. 



Marine Biological Laboratory, 

 Woods Hole, Mass. 

 July 7, 1914. 



LITERATURE CITED 



Beckwith, C. J. 1914 The genesis of the plasma structure in the egg of Hydrac- 



tinia. Jour. Morph., vol. 25, p. 189. 

 Browne, E. N. 1913 A study of the male germ cells in Notonecta. Jour. Exp. 



Zool., vol. 14, p. 61. 

 LiLLiE, F. R. 1908 a On the specific gravity of the constituent parts of the egg 



of Chaetopterus, and the effect of centrifuging on the polarity of the 



egg. Science, vol. 27, p. 905. 



1908 b Polarity and bilaterality of the Annelid egg. Experiments 



with centrifugal force. Biol. Bull., vol. 16, p. 54. 

 Lyon, E. P. 1907 Results of centrifugalizing eggs. Arch. f. Entwickl., Bd. 



23, S. 151. 

 Morgan, T. H. 1910 Cytological studies of centrifuged eggs. Jour. Exp. Zool., 



vol. 9, p. 593. 



PLATE 1 



EXPLANATION OF FIGURES 



1 Normal resting spermatocyte cell, showing distribution of mitochondria. 



2 Older resting spermatocyte cell, centrifuged. The gray mass consists of 

 mitochondria. 



3 Younger resting spermatocyte cell, centttifuged, showing oil drops, and mass 

 of mitochondria against nuclear membrane. 



4 Dividing cell, centrifuged; late anaphase. 



5 Dividing cell, centrifuged; early anaphase. 



6 Dividing cell, centrifuged; polar view of metaphase. 



