288 RALPH S. LILLIE. 



In the above described experiments the total optimum period 

 of exposure to 32° is about the same {ca. 7 to 8 minutes) whether 

 the exposure is continuous or in two stages. No doubt it would 

 be possible to increase the number of stages to three or more, 

 especially if lower temperatures (31° or 30°) were used, but no 

 experiments of this kind have so far been attempted. Appar- 

 ently what is essential is that the critical process begun by the 

 warming should continue, at the given temperature, for a 

 certain definite length of time, sufficient presumably to allow 

 some critical chemical interaction to proceed to its completion. 

 It is interesting to note that a preliminary warming which is 

 too brief in itself to cause membrane-formation may nevertheless 

 have the effect of shortening the period of after-warming neces- 

 sary to cause complete development. In one experiment the 

 preliminary exposure to 32° was only 2 minutes, a time insufficient 

 for membrane-formation in more than very few eggs {ca. 1 per 

 cent.) ; these eggs, however, when again exposed to 32° for 4 

 minutes, gave a considerable proportion of larvae (5 to 10 per 

 cent.) ; while eggs exposed to 32° for 4 minutes without any 

 previous treatment formed membranes, but none developed to 

 larvae. A continuous single exposure of 6 minutes gave 25 to 35 

 per cent, of larvae; this exposure was well below the optimum 

 of 8 to 10 minutes at which 80 to 90 per cent, formed larvae. 

 This effect of the four minutes' after-exposure on eggs which 

 otherwise showed no external change indicates that membrane- 

 formation is not in itself a critical event, but simply an expression 

 of a partial initiation of the general developmental process: 

 i. e., a partial activation has been accomplished, enabling the 

 egg to carry out a few of the early steps in development. 



Since brief exposure to weak fatty acid solution has the same 

 physiological effect on the egg as brief warming, it would appear 

 that the essential change produced in the egg-protoplasm by 

 either form of treatment is the same; if so, after-treatment with 

 warm sea-water should have a similarly favorable effect on eggs 

 in which membranes were formed by fatty acid. The following 

 series of experiments shows that this is the case' (Table XIV.). 

 The eggs, after membrane-formation by butyric acid, were after- 

 treated with warm sea-water (32°) for periods ranging from 2 



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