THE BIOLOGY OF THE CELL SURFACE 



to experimental means for eliciting development which now 

 follows will give evidence against this view and prove that 

 the egg's response like that in fertilization is cytoplasmic. 



Above I called attention to the interesting case of the 

 starfish egg. Like that of many other eggs, its germinal 

 vesicle breaks down when the egg comes from the female 

 into sea-water. But whereas other eggs of this class do not 

 develop farther unless they are fertilized, the unfertilized 

 egg of the starfish completes both maturation-divisions. 

 This fact suggests that this egg is extremely unstable and 

 lies close to being normally parthenogenetic. It is not 

 astonishing, therefore, that the starfish egg is found to be 

 most easily induced to parthenogenetic development by 

 one of several means. 



The knowledge that sea-water charged with carbon-diox- 

 ide brings about the development of eggs of a starfish, 

 Asterias glaciaiis, we owe to Delage^ who was able to rear 

 the parthenogenetic larvae through metamorphosis. This 

 method has been successfully employed by others- on eggs 

 of this as well as on those of other species of Asterias. 

 Development also results if one crowds a large number of 

 eggs in the stage of first maturation in a small volume of 

 sea-water and leaves them there for about an hour — in this 

 case the result is due to carbon-dioxide produced by the 

 eggs. In my judgment the parthenogenetic development 

 obtained by Mathews^ through shaking eggs of Asterias 

 forbesii is likewise to be attributed to carbon-dioxide pro- 

 duced by crowding the eggs; shaking of maturing eggs, in 

 my experience at least, is without avail unless the eggs be 

 crowded. 



If a thin suspension of maturing unfertilized eggs of this 

 species is placed in large volumes of sea-water in uncovered 



1 Delage, igo8, igio. 



- Buch^ier, igii and others. 



•■' Mathews.^ igoi. 



212 



