6 ART. 3. — S. IKEDA : CONTRIBUTIONS 



toward the egg periphery. In some cases, however, the third 

 cleavage-line appears to encircle horizontally a small area around 

 the upper pole of the egg as recorded in my former paper. There 

 are many other individual differences with respect to the third 

 cleavage. The fourth cleavage appears, in general horizontally 

 encircling an area which takes in about two-thirds of the upper 

 hemisphere (Figs. 5 and 6). It does not appear as a continuous 

 line, but as seven or eight separate lines or pits upon the earlier 

 (first, second, and third) cleavage-lines, and at nearly equal dis- 

 tances from the upper pole. The segmentation-lines which appear 

 later than this are very irregular and are confined mostly within 

 the circle formed by the fourth cleavage-line. Most of the later 

 cleavage-lines including even the second and third can not be 

 traced clearly to the lower pole of the egg. Indeed it is the first 

 only which can be distinctly seen to reach the lower pole. In 

 living eggs of later stages, all the cleavage-lines become super- 

 ficially indistinct in the lower hemisphere while they are distinct 

 in the upper hemisphere (Fig. 7), so that the eggs of these 

 stages present the appearances of meroblastic forms, though when 

 examined in sections they are seen to be truly holoblastie. 



During the earlier part of the season, segmentation is finished 

 at the end of the second day after deposition. Later, with the 

 rise in the atmospheric temperature, the process is gone through 

 faster, so that it is finished at the end of the first day after 

 deposition or even in less time. Toward the end of the seg- 

 mentation process, a part of the the upper hemisphere of the 

 egg becomes gradually translucent (Fig. 8). This area which is, 

 as a rule, circumscribed by a circular depression (Fig. 9) occupies 

 from the first nearly two-thirds of the upper half, und cor- 

 responds approximately to the circle enclosed by the fourth 



