148 Edward Hindle 



lassema, and other investigators, but are opposed to the theory of 

 DEL AGE. 



LOEB ('09) has shown that in sea-urchins, and many other classes 

 of animals, the developmental effects of fertilization consist essenti- 

 ally of two processes; first, in an alteration of the cortical layer of 

 the egg, presumably a cytolysis, resulting in the formation of a mem- 

 brane; and, secondly, in a modification of the processes of oxidation, 

 probably by the destruction of some substance within the egg that 

 is injurious to the synthetic processes started by the membrane 

 formation. 



The first process may be effected by any cytolytic agent and if 

 cytolysis is not carried too far the egg begins to develop. Among 

 the agents that are able to cause membrane formation in the egg 

 the following may be mentioned: In the first place we have those 

 substances having a specific cytolic action on cells in general, such 

 as saponin, solanin, digitalin, bile -salts and soap; then we have 

 the simple fat solvents such as benzol, toluol, amylen, and chloro- 

 form, which cause membrane formation very rapidly and, in addition, 

 completely cytolize the eggs in a short time; alcohol, ether, and 

 even distilled water are also effective ; but the most convenient agents 

 to employ are solutions of alkalies, or of acids, especially monobasic 

 fatty acids. 



In the presence of free oxygen this membrane formation starts 

 the oxidations underlying the synthesis of nucleins and other pro- 

 cesses of development, and in some forms (e. g. Thalassema and 

 Asterina) the eggs continue to segment normally and develop into 

 free swimming larvae. But the eggs of sea-urchins seem to contain 

 some substance that has an injurious effect upon the syntheses under- 

 lying development. By the time that the first spindle is formed the 

 eggs begin to disintegrate and at ordinary temperatures (15 C.) the 

 majority do not complete the first division. It is true that by keep- 

 ing them at a low temperature (2 5 C.) they may segment normally 

 for some time, but only a very small percentage develop into blas- 

 tulae. Therefore a second process is necessary in order to eliminate 

 this disturbing factor of development. After membrane formation, the 

 subsequent treatment with hypertonic sea water, containing oxy- 

 gen, for from thirty to fifty minutes is sufficient to destroy this in- 

 jurious substance, and if the eggs are then transferred back into 

 ordinary sea water development proceeds regularly and a large per- 

 centage develop into normal larvae. Instead of employing a hyper- 



