32 ART. 3. S. IKEDA I CONTRIBUTIONS 



at 4:45 p.m. it had rotated about 20° in the opposite direction i.e. 

 obliquely ventrad. By careful examination, I was convinced that 

 such unexpected movements of the egg were due to accidental 

 causes, such as the too rapid rotation of the mirror dish, since the 

 vitelline membrane and the outer envelope had become very loose 

 by absorbing a large amount of water. By allowing the egg to 

 stand quietly without any disturbance for ten or fifteen minutes, 

 it gradually returned to its normal position and was rotating in 

 the usual way. Thus, at 5:10 p.m., the dorsal lip had returned 

 to about 50° below the equator, and the ventral lip was at the 

 resting point of the egg, the blastopore being thus 40° in its 

 diameter. 



At 8:30 on the next morning (the fourth day), the ventral lip. 

 of the blastopore was 6° or 7° posteriorly from the resting point 

 of the egg, while the dorsal lip had again grown downwards 4° or 

 5°, showing that very slight, if any, egg rotation had occurred 

 during the night, although the blastopore had lessened 3° or 4° 

 in its diameter. This was probably due to the fact that the 

 temperature was low during the night. During the day, I was 

 not able to observe the egg up to 2 p.m., when the blastopore 

 had already nearly closed and the yolk-plug had mostly withdrawn 

 into the interior. The neural groove and fold were also recog- 

 nizable. The arc of rotation in this egg was evidently less than 

 in the first, and the final position of the closed blastopore did 

 not coincide with the first starting point of the dorsal lip, being at 

 about 55° below the equator. The difference between the former 

 and the latter was thus about 25°, and the arc passed over by 

 the egg rotation was about 35°. I thought it quite probable that 

 in this case the rotation would be continued after the complete 

 closure of the blastopore, as in one of the Bhacophorus eggs, but 



