ARTIFICIAL PARTHENOGENESIS IN ARBACIA. 145 



No. I, 7 gastrulae out of 16, 43 per cent. 



No. 2, 9 gastrulae out of 90, 10 per cent. 



No. 3, 10 gastrulae out of 109, 10 per cent. 



Examined again twenty-six hours later with the following 

 results : 



No. i, 8 plutei and 12 gastrulae out of 27, 74 per cent. 



No. 2, i pluteus out of 42, .02 per cent. 



No. 3, no living forms out of 39. 



This difference in the ratio of development is probably due to 

 the noxious effects of the undeveloping eggs in the solution. 

 This being the case a frequent change of the concentrated solu- 

 tion might raise the percentage, for while the sterilized sea-water 

 was changed repeatedly the concentrated water was not changed 

 at all during the period. The difference in results was evident 

 at this stage, that is, the two lots of eggs when removed from 

 the condensed solution showed a difference in behavior. As just 

 noted, the eggs from the cultures containing the smaller number 

 showed a larger percentage of segmentation. Cultures No. 2 

 and No. 3, having same ratios, gave similar percentages. 



State of Development. - - Wilson x has observed that the eggs of 

 Toxopncitstcs which would not fertilize with spermatozoa gave 

 some of the best results obtained with the magnesium solution. 

 Delage ~ notes in Strongylocentrotus that frequently eggs which 

 will not develop by artificial parthenogenesis are readily fertilized 

 by spermatozoa. A number of observers have noted the wide 

 variation in the behavior of the eggs of different females. Some 

 eggs do not develop at all, others give large percentages of active 

 larvae. A case in point : An experiment with a large female, the 

 eggs of which by their number, color and the freedom with which 

 they came from the ovary the ovaries in such cases when 

 placed in sea-water lose form and become a mass of eggs - - seemed 

 to signify that the eggs were fully matured (ootids). As further 

 proof, the greater part of these eggs were fertilized with sperma- 

 tozoa, this resulted in the normal development of all the eggs ob- 

 served. The remainder of the eggs were subjected to the influence 



1 E. B. Wilson, "A Cytological Study of Artificial Parthenogenesis in Sea-urchin 

 eggs," Archivf. Entwickelun^smeth., XII., 4, 1901, p. 535- 



2 Delage, Y., " Etudes Experimentales sur la Maturation Cytoplasmique Chez les 

 Echinodermes," Archiv d. Zool. Exper. et Generate, 3, Sen, IX., 1901, p. 300. 



