29O E. E. JUST. 



speaking of Arbacia he says : " Since the membrane called forth 

 by butyric acid is not always plainly visible, it is a prerequisite 

 that always one set of such eggs should be set aside as controls 

 to ascertain whether or not all the eggs disintegrate rapidly (if 

 no second treatment is given them) . Only if they all disintegrate 

 rapidly have we any guarantee that in all of them the membrane 

 formation has been effective" (Loeb, '15, page 262). Now, 

 curiously enough, Loeb never saw membrane formation in 

 Arbacia for he tells us of this egg : " When transferred to sea- 

 water, they did not form a conspicuous fertilization membrane 

 as did the eggs of S. purpuratus under the same circumstances, 

 but only a fine gelatinous layer which was not easily visible" 

 (Loeb, '13, page 71). Since, however, one can with proper ex- 

 posure to butyric acid obtain very beautiful membranes in Ar- 

 bacia and can obtain " the fine gelatinous layer " only through 

 over-exposure it is clear that Loeb was dealing with over-exposed 

 eggs which tend to disintegrate rapidly. Thus, according to Loeb 

 over-exposure hastens cytolysis in Arbacia. 



Again, Moore, working likewise with Arbacia, states : " Eggs 

 exposed to butyric acid for slightly longer than the optimum time 

 for membrane production do not produce membranes yet they 

 cytolyze even more rapidly than in cases where membranes have 

 been produced . . . they will many times have almost completely 

 disintegrated when the first signs of cytolysis appear in eggs pro- 

 vided with membranes" (Moore, '16). Here, again, is noted a 

 sharp difference between properly exposed and over-exposed 

 Arbacia eggs. 



Finally, Herlant ('17) working with Paraccntrotus makes the 

 point that it is not the formation of membranes that brings about 

 cytolysis, for these eggs with butyric acid membranes may with- 

 stand the action of sea-water for twelve to fifteen hours before 

 the onset of cytolysis. The egg cytolyzes despite the presence of 

 the membrane because of internal changes due to nuclear activity. 



In conclusion, then, we find that these facts taken together 

 indicate that there is a clear cut difference between the butyric 

 acid treated egg with a membrane and the over-exposed egg with 

 a jelly-like cortex. The over-exposed egg is an egg in the initial 

 stages of cytolysis, its jelly-like cortex marks the beginning of 



