200 GERM-CELL CYCLE IN ANIMALS 



work of Ancel, using Helix arbustorum for his material. 

 He confirms many of Ancel's results, objects to others, 

 and adds certain new observations. The germinal 

 epithelium is considered by Buresch to be a syncy- 

 tium containing both in young and old specimens 

 three sorts of cells, indifferent cells, egg cells, and 

 nurse cells. Likewise spermatogonia are present 

 not only in young but also in fully developed her- 

 maphroditic glands. This is contrary to Ancel's idea 

 of successive transformation. Buresch' s view is 

 indicated in Fig. 59. Here the vertical row of circles 

 represents the nuclei of the syncytial germinal epithe- 

 lium, some of which, as at ra, change to indifferent 

 germ cells. These may pass into the lumen of the 

 acinus as spermatogonia of the first order (Sg. I) 

 and divide to form spermatogonia of the second order 

 (Sg. II) which grow into spermatocytes (Sc) ; sper- 

 matozoa are derived from these in the usual manner. 

 Other indifferent germ cells remain in the wall, as at 

 w, and grow into oocytes, and a third class of cells 

 become nurse cells (n). In Fig. 58, A is shown a 

 nucleus of the germinal epithelium about 4 microns 

 by 6 microns in size. During differentiation into an 

 indifferent germ cell (Fig. 58, (7) the chromatin forms 

 a nucleolus, and both nucleus and nucleolus increase 

 in size until the former reaches a diameter of about 7 

 microns. Those indifferent germ cells that are to 

 produce spermatozoa separate from the epithelium 

 with a small amount of cytoplasm and fall into the 

 lumen of the acinus as spermatogonia of the first 

 order (Fig. 58, D). These divide to form spermato- 



