ACTIVATION OF UNFERTILIZED STARFISH EGGS. 27 1 



time when starfish eggs were unusually abundant and favorable. 

 On account of the relative completeness of my observations at 

 this temperature, the general results of these experiments will be 

 described in some detail. 



The exposure required for membrane-formation is about half 

 that at 31°. An exposure of 3 minutes typically forms mem- 

 branes in all normal eggs, and one of 2 minutes is usually sufficient 

 to produce this effect in a minority and sometimes in a majority 

 of eggs. From 3 minutes on the conditions remain normal for 

 membrane-formation until the exposure is prolonged to 12 or 

 15 minutes, after which in a certain proportion of eggs membranes 

 tend to separate imperfectly or even fail to form. In most series 

 exposures longer than 15 minutes were not used, since eggs so 

 treated never form larvae; in one series, however, eggs were 

 exposed for 27 minutes, at which exposure nearly half failed to 

 form membranes. This decline in membrane-formation when 

 exposures are prolonged beyond a certain maximum is general 

 for all temperatures (cf. also the series at 30°, 31° and 33°) ; the 

 fact is interesting since it indicates that the process is not a direct 

 effect of the high temperature but constitutes an active response 

 — probably in the nature of a secretion — on the part of the egg. 



The optimum exposure for inducing complete development at 

 32° varies between 6 and 8 minutes, and with this exposure the 

 great majority of normal eggs cleave and develop to larval stages. 

 Many of the gastrulae and Bipinnariae thus obtained are appar- 

 ently quite normal and swim freely at the surface of the water. 

 The rate of development is, however, always slower than that 

 of sperm-fertilized eggs; relative slowness of development seems 

 in fact to be a constant peculiarity of parthenogenetically acti- 

 vated eggs.^ Exposures well above the optimum are followed 

 by imperfect or delayed cleavage and failure to develop beyond 

 early stages. 



Table IV. gives a summary of the results of the six successive 

 series referred to above. The approximate proportions of eggs 

 forming free-swimming larvae are given; the conditions of mem- 

 brane-formation have already been sufficiently described. 



1 This has been my uniform experience since I began studies of this kind, and 

 apparently the experience is general. This suggests strongly that the spermatozoon 

 contributes to the egg material which is utilized in normal development. 



