264 RALPH S. LILLIE, 



exposure to hypertonic or cyanide-containing sea-water. The 

 starfish egg can, however, be made to develop completely without 

 the necessity of any such after-treatment, simply by sufficiently 

 prolonging the exposure to the membrane-forming agent. An 

 exposure of 8 minutes to 32° is followed not only by membrane- 

 formation, but by cleavage and development of all normal eggs 

 to larval stages {cf. page 271). Similarly, exposure to n/260 

 butyric acid for a sufficient period — varying from 6 to 10 minutes 

 — also causes all eggs to cleave and develop to larvae (c/. p. 282). 

 Over-exposure, if slight, is followed in both cases by a decrease 

 in the proportion of favorably developing eggs; and if well- 

 marked, by complete failure of development and early break- 

 down. The only noteworthy difference that I have observed 

 between the effects of the two agents is that the time-relations 

 in the case of exposure to fatty acid have been somewhat more 

 variable than in the case of exposure to a definite temperature 

 such as 32°. Thus in some experiments eggs have exhibited a 

 considerable proportion of favorable developments after only 

 one minute's exposure to weak fatty acid solutions.^ In such 

 cases however the concentration of acid was somewhat higher 

 (3 c.c. n/io fatty acid plus 50 c.c. sea-water) than in the experi- 

 ments described above. In last summer's experiments (in which 

 the fatty acid was always used in nf26o concentration) the curves 

 relating time of exposure to the proportion of eggs forming 

 larvae were virtually identical in form with the two agents, — a 

 fact showing that the essential effects produced by both types 

 of treatment are the same. 



The fact that a properly timed single exposure to warm sea- 

 water or fatty acid solution causes complete development 

 suggests that the necessity for a supplementary after-treatment 

 {e. g., with hypertonic sea-water), in the case of eggs in which 

 fertilization-membranes have been formed by brief preliminary 

 exposure to a cytolytic agent, depends simply on the incomplete- 

 ness of the change induced in such eggs by the membrane-forming 

 treatment. The fact that by sufficiently prolonging this treat- 



1 See the experiments described in my recent paper in the Journal of Experi- 

 mental Zoology, 1913, Vol. 15, pp. 41, 42. Starfish eggs exposed for i minute to a 

 mixture of 3 c.c. w/io acetic or butyric acid plus 50 c.c. sea-water (M/176 acid) gave 

 in several cases 20-30 per cent, of larvae and in one case 70-80%. 



