INITIATION OF DEVELOPMENT IN THE EGG OF 



ARBACIA. 



III. THE EFFECT OF Arbacia BLOOD ON THE FERTILIZATION- 

 REACTION. 



E. E. JUST.i 

 ROSENWALD FELLOW IN BIOLOGY, NATIONAL RESEARCH COUNCIL. 



I. 



During May, 1921, Arbacia examined at Woods Hole, Mass., 

 were found to be immature. Thus, on May 15, bits of the gonads 

 examined under the microscope contained only immature eggs 

 devoid of color. The testes showed no mature sperm. Toward 

 the end of May a few females were found in which the eggs were 

 undergoing maturation. Early in June (June i to 8) the eggs 

 gave very low per cent, fertilization. From this time on eggs 

 exuded through the genital pores steadily increased in fertiliza- 

 bility. Eggs taken from the ovaries, on the other hand, were 

 largely immature; their fertilization per cent, was lower than that 

 of eggs that exuded from the genital pores when the animals were 

 carefully cut around the peristome. Toward the end of July the 

 high fertilization capacity of the shed eggs (i.e., eggs that exuded 

 from the genital pores when the animals were carefully cut around 

 the peristome) fell off. From July 20 to the end of the season 

 the fertilization capacity of shed eggs from a given female was 

 found to be markedly inferior to eggs taken from the same female 

 by cutting up the ovaries in sea-water. There was thus found 

 during the first part of the season in the case of shed eggs a rise 

 in fertilizability followed by a fall. Parallel with this fall was 

 found a rise in fertilizability of eggs from the ovaries which dur- 

 ing June were largely immature. It was thus found that eggs of 

 Arbacia of high fertilization capacity may be obtained at Woods 

 Hole throughout the season provided shed eggs are used during 

 the early part and eggs from the ovaries during the later part of 



1 Zoological Laboratory, Howard University. 



411 



