Development without Membrane Formation 223 



rated by some work of Herbst^ to which we shall return later. 

 Herbst put the eggs of Sphaerechinus in 50 c.c. of sea-water +3c.c. 

 N/10 acetic acid for two to eight minutes. The eggs formed, 

 if I interpret Herbst correctly, not a typical membrane, but a 

 fine gelatinous film, and upon transference to normal sea-water 

 a few of them developed into larvae, without it being necessary 

 to expose them first to hypertonic sea-water. I am inchned to 

 believe that in all cases in which an unfertilized sea-urchin egg 

 has been caused to develop, a typical or atypical membrane had 

 been formed. 



The reader will notice that in these cases the eggs developed 

 without any treatment with a hypertonic solution, at room 

 temperature. We shall see later that this is not uncommon 

 in the egg of the starfish. We must conclude that in such cases 

 the corrective effect is produced by changes taking place inside 

 the egg itself. The situation is comparable to that in the 

 experiments in which the hypertonic solution was replaced by 

 a treatment of the eggs with lack of oxygen. In this case we 

 are also forced to assume that the egg itself was able to 

 produce the substance which counteracts the threatening disin- 

 tegration. In the eggs of some species, and possibly of some 

 strains or individuals, this substance can possibly be formed 

 under normal conditions and for such eggs the process of mem- 

 brane formation may suffice, the egg being able to furnish the 

 corrective effect or being naturally more resistant. 



'Herbst, " Vererbungstudien IV," Archiii f. Entwicklungsmechanik, XXII, 

 473, 1906. 



