148 



and at right angles' to the last. The excentricity of the nuclei is 

 scarcely apparent at this stage, but can often be seen. The division 

 is generally into four equal cells but sometimes the cells are smaller 

 at the nucleated end. After this stage is reached the compression 

 was gently removed without turning the egg. The third cleavage then 

 came in horizontally or at right angles to the preceeding two, in other 

 words the second and third planes of cleavage have come in re- 

 versed order. The micromeres form at the next cleavage and appear 

 at the pole opposite to the early nuclei i. e. in their normal position 

 and not in the vertical line through the middle of the egg and not 

 at the crossing line of the first and second furrows, but 

 where the first and third furrows cross, again pointing to 

 an interchange in time of appearance of the second and third furrows. 



Fig. 4. 



Another observation calls for particular attention in this con- 

 nection. In one egg that had reached the four cell stage under com- 

 pression (as above) and then had the pressure removed, the eight 

 cell stage was produced not by horizontal cleavage planes, but by the 

 formation of its micromeres at once. 



Two micromeres formed in the normal position for the micro- 

 meres by vertical furrows and four macromeres were produced ad their 

 proper pole by radial divisions. A perfect half sixteen cell stage was 

 formed at the eight cell stage. Either the third cleavage has dropped 

 out to appear later so that the fourth cleavage planes has come in 

 prematurely producing the micromeres ; or the pressure may have been 

 removed only from one side of the egg completely and the whole egg 

 has reacted as a half. The first alternative seems more probable. 



C. 

 In the Journal of Morphology, Vol. Ill, No. 2, Dr. Jacques 

 Loeb has described an interesting experiment by means of which he 



