ACTIVATION OF UNFERTILIZED STARFISH EGGS. 275 



It is interesting to note that the effects produced by weak fatty 

 acid solutions (n/260 butyric acid) on unfertilized starfish eggs 

 also vary with the time of exposure in a manner closely similar 

 to that just described. Brief exposure causes membrane-forma- 

 tion followed by irregular change of form and breakdown without 

 development, while longer exposure induces not only membrane- 

 formation but cleavage and development to larval stages; still 

 longer exposure is again unfavorable. Eggs in which membranes 

 have been formed by the minimal exposure to fatty acid may be 

 made to develop by the above forms of after-treatment. The 

 effects of the two agents, warm sea-water and weak butyric 

 acid solution, seem in fact to be identical in every essential 

 particular, and the one may be substituted for the other without 

 altering the effect on the egg (c/. Tables XIV. to XVII.) . Experi- 

 ments showing this parallelism will be described in detail later. 

 There is in fact every indication that the underlying physio- 

 logical process which enables the egg to continue normal develop- 

 ment is of the same nature as that which induces simple mem- 

 brane-formation, the only difference being that the duration of 

 the process must be considerably longer in the second case than 

 in the first. The temperature-coefficients of both effects indicate 

 the same, as will appear below (cf. Table X.). The possible 

 nature of this process will be discussed in the concluding section 

 of this paper. 



Treatment with sea-water at 33° gives similar results to those 

 above described, except that the times required to produce a 

 given physiological effect are only a little more than half as 

 long as at 32°. An exposure of from one to one and a half 

 minutes is needed to call forth membrane-formation in the 

 majority of eggs. Four series of experiments with normal eggs 

 were performed at this temperature, and in every series the 

 great majority of eggs formed larvae with the optimal times of 

 exposure. In these series the earlier transfers from the warm 

 sea-water to normal temperature were made at half-minute 

 intervals. The results are summarized in Table VI. 



In all of these series the proportion of favorably developing 

 eggs is high with the optimum exposures of 4}^ to 5)^ minutes. 

 The series of June 15 is unusual in that nearly all of the eggs 



