382 Ralph S. Lillie 



No membrane was formed. In one series of experiments, eggs 

 in early maturation, stages (at which time membranes are most 

 readily formed) formed in some instances membranes on exposure 

 to 45° for 15 seconds; exposure to the same temperature for 30 

 seconds was followed by breakdown without membrane-formation. 

 Temperatures of 45° and higher are thus rapidly destructive, as 

 in the case of sea-urchin eggs; but very brief exposures may produce 

 some of the effects (as membrane-formation) of more favorable 

 conditions. 



Temperatures of 40° and lower were then tried. The earliest 

 visible effect of brief warming at such temperatures is the forma- 

 tion of the fertilization membrane. The production of this mem- 

 brane appears to be associated with the removal of certain hin- 

 drances to further development (p. 385), and accordingly it may 

 be regarded as the first visible sign of developmental changes 

 in the egg. The structure is produced with remarkable ease by 

 momentary exposure of eggs to the action of warm sea-water; yet 

 it is significant that temperatures above a certain maximum \ca. 

 45°), acting for more than a few seconds, fail to cause its produc- 

 tion. Apparently some ferment-action, rather than the direct 

 effect of the heat, is concerned. It also fails to be produced at 30° 

 unless possibly the exposure is very prolonged. I have made few 

 observations with temperatures lower than 35°. The temperature 

 relations of this phenomenon ought perhaps to be more thoroughly 

 investigated. 



The following table summarizes the results of three series of 

 experiments covering a considerable range of temperatures. They 

 illustrate very typically some of the conditions of membrane-pro- 

 duction in starfish eggs. 



