PAR THENOGENESIS 



cient. We shall soon learn that eggs of sea-urchins which, 

 with the above discussed osmotic method, develop abnor- 

 mally, are no exception to this rule. 



3. Hypertonic sea-w^ater is most generally effective 

 although the result is not the same qualitatively for each 

 species of eg^. 



4. No experimental means is limited in its action to eggs 

 of one fertilization-class only. 



No. 4 requires comment. If we arrange eggs into four 

 classes, on the basis of their fertilization-moment, we do not 

 find that for each of these classes one special treatment is 

 alone successful. Heat, for example, is as successful on 

 the egg of Nereis in the germinal vesicle stage as on that 

 either of the worm, Chaetopterus, or of the clam, Cumingia, 

 both in the stage of first maturation. On the other hand, 

 eggs of the same fertilization-class do not always respond 

 to the same means. Hypertonic sea-water does not induce 

 cytoplasmic division in the egg of Nereis, but does in the 

 egg of Alactra, which like that of Nereis is fertilizable in 

 the germinal vesicle stage. Acid-solutions in sea-water fail 

 to Initiate development in the egg of Nereis; they call forth 

 development in the egg of Thalassema^ fertilizable like 

 that of Nereis in the germinal vesicle stage. Moreover, 

 consider the egg of the starfish. It responds best when in 

 that stage, first maturation, which is optimum for its fer- 

 tilization. Carbon-dioxide, butyric acid or heat alone is 

 sufficient for eliciting complete response: membrane-separa- 

 tion, cleavage and vigorous larvae. Butyric acid alone, 

 however, does not initiate development in eggs of other 

 species in whatever stage of maturation they are fertilizable. 

 Shaking, which suffices for the induction of development of 

 the starfish egg, is without effect on other eggs fertilizable 

 in the same stage, though In the egg of Nereis it does cause 

 the break-down In the ectoplasm and the dissolution of the 

 germinal vesicle. 



