FURTHER STUDIES ON THE PARTHENOGENETIC 

 DEVELOPMENT OF THE STARFISH EGG. 



D. H. TENNENT. 



The results of investigations described in an earlier paper 1 led 

 me to the view that possibly a conjugation of egg and sperm 

 chromosomes, similar to that apparently occurring in starfish 

 eggs that had been treated with C0 2 and subsequently fertilized, 

 might be found to occur in normally fertilized eggs. 



As I suggested in the paper mentioned, it would be necessary, 

 in order to settle the question raised, to reexamine the normal 

 fertilization and cleavage stages or to make a study of the forma- 

 tion of the germ cells in the starfish. 



This paper deals with observations made in accordance with this 

 plan and with some further observations made on starfish eggs, 

 developing as a result of treatment with C0 2 . The material for 

 the investigation was obtained while I was occupying a room at 

 the Marine Biological Laboratory, Woods Hole, during a portion 

 of the summer of 1906. 



I found, soon after beginning a study of fertilized starfish eggs. 

 that the equatorial plate of the first cleavage spindle contained, 

 with variations which I shall mention later, in eggs from some 

 individuals 18 chromosomes, and in eggs from other individuals 

 36 chomosomes. I have as yet been unable to correlate this 

 difference in the number of chromosomes with the common star- 

 fishes of the Woods Hole region, Asterias forbesii and Asterias 

 vulgaris? although it is probable that such a relationship will be 

 established. 



The study <3f the fertilized eggs proved puzzling, and it was 

 not until I had made an investigation of the spermatogenesis of 

 Asterias vulgaris and a reexamination of eggs developing par- 

 thenogenetically after treatment with C0 2 that I was able to find 

 a solution for the problem under consideration. 



1 " Studies on the Development of the Starfish Egg," D. H. Tennent and M. J. 

 Hogue, Journal of Experimental Zoology, Vol. I II. ( 1906). 



2 Clark, "The Echinoderms of the Woods Hole Region," Bull. U. S. F. C, Vol. 

 XXII. (1902), pp. 553-554- 



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