2j6 HELEN DEAN KING. 



entire day, failed to show any marked acceleration in the develop- 

 ment of the great majority of the eggs in the cystin solution. 

 Twenty hours after the experiment began swimming larva? were 

 found at the surface in both cultures, so in this instance the 

 development of the blastulae was not retarded by the cystin. 

 The solution was ultimately harmful, however, as all of the 

 larva? in the cystin culture died within thirty-six hours, while 

 those of the control developed into plutei that lived for several 

 days. No unusual types of larvae were noted among the living 

 forms, and none were found in microscopic preparations of the 

 older embryos. 



The Arbacia eggs wvith which Mathews experimented were 

 undoubtedly in a very different physiological condition from 

 those that I used, for Mathews states that in the control lots 

 for his experiments "hardly a pluteus was to be found and these 

 few were generally abnormal." In both of my control cultures 

 the great majority of the eggs formed normal plutei that lived 

 for some days. With such a great difference in the lots of eggs 

 experimented upon it is not surprising that the results do not 

 agree, since the reaction of eggs to any external stimulus depends, 

 to a considerable extent, upon the particular physiological con- 

 ditions existing in the eggs at the time that the stimulus is applied. 



Leucin (CcHisNOo). By the use of a weak solution of "impure 

 leucin" Mathews changed the course of development of the eggs 

 of Arbacia so that many of the embryos were totally unlike 

 Arbacia larva?. "In many, cvagination of the entoderm instead 

 of invagination, took place. A few developed a ciliated band 

 in the shape of the star-fish bipinnaria. . . . Another form was 

 perfectly spherical with a single ciliated band about the middle. 

 It looked in its external form like a small trochophore." Un- 

 fortunately, it was not possible to obtain any of the impure 

 leucin with which Mathews produced these remarkable forms of 

 Arbacia larva?, and the leucin with which I experimented was 

 presumably pure. 



Solutions of various strengths (2, I, \, yg- and $-$ per cent.) 

 were used on batches of eggs that were fertilized at 11.30 A.M. 

 on the morning of July 16, 1909. The eggs in all of the cultures 

 began segmenting at the same time as those in the control lot, 



