176 HENRY J. FRY. 



Embryos were reared in 5 cc. round-bottom salt cellars under 

 the conditions described by Tennent ('10). Great care was 

 taken to use sterilized sea water, to change it several times a 

 day, to prevent evaporation, and to keep it at the temperature 

 of the running sea water in the aquaria. 



The blastulae appeared quite regular but were more frail and 

 delicate than normal ones. Most of them died at about twelve 

 hours. Mesenchyme cells were not observed. Five blastulae 

 lived about two days; they were top swimmers, but became 

 opaque and underwent no invagination. 



In his final work Boveri ('18) came to the conclusion that 

 completely enucleated eggs of Sphser echinus, as identified by the 

 small size of the haploid nuclei, when activated by Echinus 

 sperm rarely produce a gastrula and seldom, if ever, produce a 

 pluteus. Taylor and Tennent ('24) secured but one blastula, 

 and it did not gastrulate, in the cross between enucleated 

 Lytechnius eggs and Tripneustes sperm. The present experiment 

 yields a similar result since the forty-six blastulae failed to 

 gastrulate. 



Enucleated eggs of Echinarachnius when activated by Arbacia 

 sperm produce blastulae that do not gastrulate whereas whole 

 eggs similarly activated produce gastrulae and plutei. This 

 difference in development between enucleated eggs and whole 

 ones when cross fertilized might be attributed to the general 

 harmful effects of enucleation involving general maltreatment 

 and the loss of some cytoplasm. This is probably not the cause, 

 however, since the enucleated eggs are in a sufficiently normal 

 condition to be activated by the sperm, to effect cleavage, and 

 to form blastulae. The probable explanation of the difference 

 in development lies in the fact that the whole eggs contain a 

 haploid set of their own chromosomes that normally function 

 in that cytoplasm, in addition to the other set of another species 

 introduced by the sperm, whereas the enucleated eggs contain 

 only the chromosomes of another species functioning in an alien 

 cytoplasm. The experiment demands that the two species used 

 shall not be too closely related, for they must be sufficiently 

 separated to have different pluteus characteristics in order that 

 the respective roles of maternal cytoplasm and paternal chromatin 



