8o 



MARY GRACE SPRINGER. 



Conclusion. The table shows a very slight retardation in the 

 early cleavage rate of A, B and C, and a greater amount of re- 

 tardation in the later stages, especially at the early gastrula stage. 

 D was very markedly retarded. 



A very unusual proportion of exogastrulse was found in all 

 the cultures. There was even a small proportion in the controls. 

 The reason for this is unknown. It happened that this particular 

 series of experiments was carried on during the hottest days of 

 the summer, but the bowls were kept in the water table, and the 

 temperature of the room was not above 23 C. Later experi- 

 ments failed to show an equally high percentage of exogastrulse, 

 although they were carried on under conditions as nearly identical 

 as possible. The only explanation to be offered is that there 

 may have been some variation in the eggs of the particular female 

 used which caused them to evaginate instead of invaginate. 



The question of whether these abnormal cultures of exogas- 

 trulse could possibly be influenced to develop normally if extract 

 of larva? at the same stage was added came up at this point. Of 

 course it is obviously improbable that in making the extract one 

 would at the first trial secure larvae at the identical point of de- 

 velopment of those in the culture. The eggs in the culture were, 

 however, centrifuged, the stale water decanted, and fresh water 

 added. Numerous trials of extracts made up of embryos at dif- 

 ferent points in the same general developmental stage, and in 

 preceding and succeeding stages were used. In no case did the 

 exogastrute proceed with their development. 



Scries 32. 

 TABLE III. 



