ACTIVATION OF UNFERTILIZED STARFISH EGGS. 265 



merit one can induce complete development in all eggs indicates 

 clearly that the after-treatment produces in the egg effects which 

 are physiologically of the same kind as those resulting from the 

 membrane-forming treatment, and not qualitatively different 

 as has usually been supposed. If this is so, we must conclude 

 that hypertonic sea-water is favorable not because it exerts a 

 "corrective" action different from that of the membrane-forming 

 agent, but simply because it enables the process started by the 

 first treatment and arrested at an unfinished stage to proceed 

 to its completion. On this view the effects of the two successive 

 treatments are simply additive. Apparently under the influence 

 of the higher temperature or the fatty acid a certain definite 

 process, which we may call the activation-process, is started 

 in the egg. This process, if it proceeds to a certain definite 

 stage, puts the egg in a condition to continue automatically its 

 development to the formation of larvae; but if the process is 

 arrested too soon (by the return to sea- water), the egg is able 

 to carry out only a few of the early steps of development, includ- 

 ing membrane-formation and perhaps a few cleavages. The 

 after-treatment merely causes the resumption of the process 

 and carries it to its completion. The unitary character of the 

 activation-process is further indicated by the fact that the tem- 

 perature-coefficients for simple membrane-formation and for the 

 complete initiation of development are the same, as will be shown 

 below. If this conclusion is correct, it should be a matter of 

 indifference whether the exposure for the required period to 

 the high temperature or the fatty acid solution is continuous or 

 discontinuous. It ought to be possible to form fertilization- 

 membranes by brief exposure to warm sea-water or fatty acid 

 followed by a return to normal sea-water, and then later to 

 complete the activation-process by a second exposure to either 

 agent for an appropriate time. This is in fact the case; all of 

 the four combinations have been tried: brief treatment with 

 warm sea-water followed by after-treatment for several minutes 

 with either warm sea-water or butyric acid solution ; and mem- 

 brane-formation by butyric acid followed by warming or a 

 second treatment with acid. All four methods give the sg.me 

 result, namely the development of a high proportion of eggs to 



