FERTILIZATION-REACTION IN ECHINARACHNIUS PARMA. 289 



turn to normal sea-water as evidenced by their low per cent, of 

 cytolysis and their retention of fertilization capacity as com- 

 pared with the control in sea-water, the writer was led to con- 

 tinue the observations during succeeding summers using also the 

 mixture two c.c. of n/io butyric acid plus fifty c.c. of sea-water. 

 Practically, if the egg does not form a membrane on removal 

 from butyric acid, it gains through this acid treatment a resist- 

 ance to the normal cytolytic action of the sea-water. 



Examination of the tabulated data likewise clearly reveals 

 that eggs exposed above one minute to the concentration of 

 butyric acid employed are seriously injured. The individual ob- 

 servations as cited do not, however, so clearly show that these 

 over-exposed eggs very early after removal from the butyric acid 

 exhibit marked cytolytic changes. And for this reason : What 

 primarily the writer aimed to determine was the point in time 

 after removal from sea-water when one hundred per cent, of 

 the under-exposed eggs (i.e., eggs that show no membranes) 

 completely disintegrate a point by no means easy to fix because 

 of the immunity against cytolysis conferred by the acid treat- 

 ment. It may be recalled, nevertheless, that attention has been 

 directed to the fact that cytolysis in the over-exposed egg begins 

 very early. In general, over-exposed eggs showing one hundred 

 per cent, thickened cortices give one hundred per cent, cytolysis 

 within two hours after treatment. This fact was clearly re- 

 vealed early in the study of the effect of butyric acid on these 

 eggs. Another characteristic of over-exposed eggs as elsewhere 

 noted (Just, '19^) is their response to shaking: the jelly-like cor- 

 tex breaks and the eggs give off buds. That is, gentle shaking 

 hastens cytolysis. In the egg with butyric acid membrane, the 

 same or even more vigorous shaking produces merely a collapse 

 of the membrane without injury to the vitellus. We must inter- 

 pret these facts as meaning that the over-exposed egg is an egg 

 in the initial stages of cytolysis the visible manifestation of 

 which is the swollen cortex that so sharply differentiates it from 

 the optimum exposed egg with its full round membrane and wide 

 perivitelline space. But this interpretation by no means needs 

 rest on the findings in Echinarachnius alone. 



In the first place, Loeb has recorded similar observations for 



