192 LILLIE AND KNOWLTON. [VOL. I. 



We do not think it possible to state any general law as to 

 the effect of supramaximal and subminimal temperatures on the 

 form of development. The effect differs surprisingly in differ- 

 ent organisms. So far as we know, most observations on this 

 point have been made by subjecting the form or eggs to be 

 experimented on to the abnormal temperature for a short time 

 only, and then allowing development to continue at a normal 

 temperature. Our observations, on the other hand, were on the 

 continuous effect of abnormal temperatures. 



Hertwig ( ? 94b) found that in twenty-four hours at o C. no 

 development took place, and that when the eggs were restored 

 to the room temperature, in some of them " a larger or smaller 

 part of the vegetative half of the egg was permanently injured, 

 so that it could not undergo cleavage and had to be gradually 

 excluded from the healthy developing parts." Schulze ('94) 

 doubts this, and concludes from his own observations " that 

 the eggs of Rana fusca in the gastrula stage can withstand 

 complete inhibition of the development (by cold) for fourteen 

 days without any sort of injury." However, it is quite certain 

 from our own observations that many eggs develop abnormally 

 at 3 C., as already noticed. 



Hertwig ('94a), p. 314, has also noticed that by raising the 

 temperature of the water in which eggs of the frog are develop- 

 ing there is a certain point at which the lower pole is first 

 injured and divides incompletely or not at all, while the black 

 pole forms a disc of small cells. 



Driesch ('93) observed that abnormally high temperature 

 caused great variations in the cleavage and partial suppression 

 of micromere formation in both Sphaerechinus and Echinus. 

 In a later study ('94) he tested the effect of abnormally high 

 temperature (30 C.) on the gastrulation of Sphaerechinus ; exo- 

 gastrulae were produced. If we suppose that the archenteron 

 grows in the direction of least resistance, we must conclude, 

 as Driesch points out, that the conditions of osmotic equilib- 

 rium within the blastula have undergone alteration as the 

 effect of the high temperature. 



