CELL DIVISION IN T.KNIA. 313 



the balancing o f results obtained from such unfavorable material 

 as that which the cestodes offer against such favorable objects for 

 cytological study as, for example, the Orthoptera. In the ces- 

 todes which I have studied, the cells, except the oocytes, are 

 much smaller than the insect cells, do not stain as readily, and 

 are often obscured by great masses of intercellular material. 



AIM. 



My aim in this investigation was to obtain definite evidence as 

 to the occurrence of amitosis in cestode tissues. Observations 

 were begun with the hope of bringing into line, in a small measure 

 at least, the account of cell division in this group with the results 

 generally obtained by workers on other forms. Lack of time has 

 prevented the investigation of many of the secondary questions 

 that have arisen. Thus no attempt has been made to give details 

 of chromosome behavior or structure, and the observations have 

 been limited to the method of cell division in the process of 

 oogenesis and in the growth of somatic cells. The discussion, 

 however, includes occasional reference to related questions. 



OBSERVATIONS. 



Oogenesis. The female sex cells in the cestodes in question 

 are by far the largest cells in the body. They are in general 

 round with a relatively large nucleus. The cytoplasm is fibro- 

 recticular and to a certain extent granular. Occasionally large 

 dark granules appear, as in Figs. 15, 16 and 17; their nature 

 has not been definitely made out, but they may be yolk nuclei or, 

 perhaps, nothing more than aggregations of smaller cytoplasmic 

 granules. Frequently they serve to obscure the process of 

 mitosis. 



No cell organs are located in the cytoplasm of the resting 

 mother cells ; but, at some time during the development of the 

 ovarian egg, a mass, probably of yolk, appears there. I have 

 not observed any regularity in the formation of this mass, for 

 some of the early oogonia have it, while it is not present in 

 some oocytes. The masses, of course, vary in size. Those 

 which are newly formed have a close resemblance with certain 

 stains to a " nebenkern," and, in fact, have been so called. They 



