INITIATION OF DEVELOPMENT IN THE EGG OF 



ARBACIA. 



II. FERTILIZATION OF EGGS IN VARIOUS STAGES OF ARTIFICIALLY 



INDUCED MITOSIS. 



E. E. JUST,i 

 ROSENWALD FELLOW IN BIOLOGY, NATIONAL RESEARCH COUNCIL. 



A few summers ago the writer made certain experiments with 

 various agents that caused the breakdown of the intact nucleus of 

 the mature uninseminated eggs of Arbacia and of Ediinarachniiis 

 with consequent liberation of the chromosomes in the cytoplasm. 

 During the season of 1921 at the Marine Biological Laboratory, 

 Woods Hole, Mass., opportunity presented itself to repeat some 

 of these experiments as part of a detailed study of the effects of 

 sea-water in varying degrees of hypertonicity on the uninseminated 

 Arbacia egg. The present paper deals with the results obtained 

 with one concentration only : sea-water made hypertonic by the 

 addition of NaCl or KC1 (in the proportion of 8 parts 2^2 M salt 

 to 50 parts sea-water). This report aims to set forth (i) that 

 exposure to this hypertonic sea-water gives cleavage and a small 

 per cent, of plutei, and (2) that eggs following treatment with this 

 hypertonic sea- water on return to normal sea- water are capable of 

 fertilization during any stage of the first cleavage mitosis except 

 the telophase. It is this second finding which would seem to make 

 this report of some interest : it suggests another method of attack- 

 ing the problem of fertilization in the egg of Arbacia. 



I. 



The initiation of cell division in the egg of Arbacia by means 

 of hypertonic sea- water is too well known to merit more than the 

 briefest description. The pioneer work on this subject is, of 

 course, that of Morgan ; it was Loeb, however, who first produced 

 larvae with this method. Wilson has given an excellent account 

 of the cytology of the egg of Toxopncu-stcs induced to develop by 



1 Zoological Laboratory, Howard University. 



401 



