ARTIFICIAL PARTHENOGENESIS IN ARBACIA. 147 



that phenomena manifested in the starfish must not be assumed 

 to occur in the sea-urchin, and further according to the same 

 author ' the eggs of Strongyloccntrotus are mature before being 

 subjected to the solution. From this it would seem that there 

 is a difference in the behavior of the eggs of Arbacia and Strongy- 

 locentrotus. In Arbacia it did not appear that in the development 

 of the egg there was only one opportune moment when the con- 

 centrated solution was effective, but rather that ovarian eggs 

 placed in the concentrated solution, were influenced to maturate 

 and that maturation brought about in this way resulted, when the 

 eggs were removed to normal sea-water, in segmentation and 

 subsequent development. Experiments with eggs apparently 

 mature frequently give small percentages, one to five per cent, 

 of larval development. This may be accounted for by the pres- 

 ence of a few oocytes in the ovaries. The difficulty in the case 

 of Arbacia is that owing to the opacity of the eggs it is not 

 possible to ascertain their exact state when placed in the con- 

 centrated solution. 



There is some evidence which probably bears upon the ques- 

 tion to be found in the examination of sections. Without enter- 

 ing into a detailed description at this time we find in iron-haema- 

 toxylin sections a heavily staining body in contact with the 

 nuclear membrane. In some cases astral rays extend out from 

 this dark body. In others these rays are absent. Later proph- 

 ases occur, such as the elongation of the nucleus with an aster 

 at each pole, followed by the mitotic figure in its various phases. 

 In other words, there appear to be processes closely resembling 

 normal karyokinesis. This conspicuous dark body shows its 

 attitude towards the nucleus in cases where the dark body has 

 failed to divide. In such cases, the nucleus is elongated on the 

 side of contact and the chromatin is aggregated on the same 

 side. It seems reasonable, therefore, to say that in these parthe- 

 nogenetic eggs there is a force whose behavior approximates that 

 of the spermatozoon. 



Briefly, then, in the sea-urchin egg maturation takes place in 

 the ovary before normal oviposition. 2 



i Ibid., pp. 296, 301, 324. 



2 E. B. Wilson, "The Cell," 1900, p. 236. 



