Nature of Formative Stimulation 



135 



An increase in temperature can also produce a cytolytic 

 effect. I have observed that at 34° or 35° the eggs of Strongylo- 

 centrotus purpuratus form often but not always a membrane 



Fig. 44 



Fig. 45 



Fig. 46 



Fig. 47 



Figs. 44-47. — Membrane formation and subsequent cytolysis of the egg 

 under the influence of the addition of a minute quantity of salicyialdehyde to 

 sea-water. Camera drawings. Fig. 44, unfertilized egg at the beginning of tlie 

 experiment. Fig. 45, membrane formation in the sahcyialdeliyde-sea-water. 

 Fig. 46, beginning of the cytolysis. Fig. 47, cytolysis completed. Tlie cytolyzed 

 egg has in tliis case an entirely different appearance from that of an egg cytolyzed 

 in saponin. 



of fertilization. Such a temperature kills these eggs almo.st 

 instantly and consequently they are no longer able to develop 

 after this treatment. The eggs of the star-fish Aster ias for- 

 besii are, however, not killed so rapidly after the membrane 



