IX 



THE EFFECT OF ARTIFICIAL MEMBRANE FORMATION 



ON THE EGG 



We shall see later that for the eggs of starfishes and various 

 annelids (Polynoe and Thalassema) the induction of artificial 

 membrane formation is sufficient to cause some of the unferti- 

 lized eggs to develop, into larvae. According to the experi- 

 ments of Herbst, to which we shall return later, something 

 similar appears to be the case exceptionally with the eggs of 

 the Neapolitan sea-urchins also. Neither the eggs of the 

 Calif ornian sea-urchins, nor those of Arbacia at Woods Hole, do 

 as a rule develop into larvae if artificial membrane formation 

 alone is produced in them. They do, however, without excep- 

 tion exhibit the initial changes of development after such 

 treatment. It depends upon the temperature how far they will 

 develop. If the temperature is very low (from 2 to 5) the eggs 

 divide very slowly and regularly, and a few may develop into 

 swimming larvae, 1 although they do not survive the blastula 

 stage. If the temperature is a little higher, some 6 to 8, the 

 eggs go into the two-, four-, eight-, and even sixteen-cell stage, 

 but no farther. At higher temperatures still, say 15 to 18 C., 

 a formation of astrospheres and nuclear division takes place; 

 but then the development comes to a standstill and the eggs do 

 not divide, but slowly disintegrate. 



The fact that the egg can develop at a low temperature to 

 the blastula stage, and that nuclear division and cell division 

 begin always after the membrane formation, proves that this 

 process suffices to set the whole apparatus of development in 

 motion. The subsequent treatment with a hypertonic solution 



1 Loeb, Untersuchungen ueber kilnstliche Parthenogenese, p. 490; Biochem. 

 Zeitschr., I, 203, 1906. 



73 



