ON THF. CTEXOPHORF FOG. 



330 



d. Experiment IV (thirty-eight cases). 



During the first cleavage various amount of cytoplasm was cut off 

 to see how cleavage goes on in nucleated fragments. Since ZlEGLER 

 ('98 p. 58) has already discovered that the micromeres are formed 

 after such an operation, this series of experiments was especially 

 directed to ascertain the size relation between the micromeres. Of the 

 thirty-eight eggs, thirty were cut horizontally at different levels and 

 the rest obliquely. 



In the case of horizontal cutting (Fig. II, 15-17; Fig. III, 1S-20), 

 we notice that in small fragments the size of blastomeres and es- 

 pecially that of the end-cells is more variable. In Fig. II 17, one of 

 the middle-cells has budded out a large micromerc, and two of the 

 end-cells have divided equally. In larger pieces the size relation 

 between the end-and middle-cells is almost normal (Fig. III. 18-20). 



Now as to the size of the micromeres. As we have already 

 seen in the foregoing experiments the micromeres vary somewhat in 

 size even in one and the same egg. In general, however, it may be stated 

 that they are proportional in size with the fragments (cf. Fig. II. 15 or 16 

 and Fig. III. 19 and 20). To a certain extent the micromeres are also 

 proportional in size to the macromeres, it is true ; those of the 

 middle-cells are usually larger than those of the end-cells. But that 

 is not always the case, since the small end-cells may sometimes pro- 

 duce relatively large micromeres (Fig. II, 16 and 17). 



Turning our attention to the relation between the size of micro- 

 meres and the quantity of the ectoplasm contained in the piece we 

 find that, contrary to our expectation, there is no such relation at all. At 

 the stage of Fig. II 1 5, a large quantity of the ectoplasm has gonedown 

 towards the macromere pole, while at the stage of Fig. II 16 (or still 

 better Fig. Ill 18 19, 20) its greater part has ascended towards the 

 micromere pole, yet, as these figures show, the sizes of the micromeres 

 are almost the same. 



