86 A. RICHARDS. 



the depression set in before the acceleration could take place and 

 during the entire course of the experiment these eggs were behind 

 both the shorter radiation and the control in development. 



As is well known temperature profoundly affects the rate of 

 cleavage, a rise causing an increase in the rate. The question at 

 once is suggested, can the temperature changes induced by the 

 conditions of the experiment account for the effects on the rate 

 as here given. There are several considerations which would 

 seem to point to an affirmative answer to this question, (i) The 

 resistance which the rays meet in passing through the protoplasm 

 of the egg would tend to cause a rise in temperature. (2) It is 

 easily conceivable that some of the energy might be converted 

 into heat energy. Rutherford has shown that radium emanina- 

 tion produces a rise in temperature of considerable extent in 

 gases through which it passes. (This is due, however, to the a 

 rays to the extent of 70 per cent, of the effect noticed). (3) 

 Finally, the histological conditions in the eggs resemble those 

 produced by allowing eggs of Crepidida to develop at a tem- 

 perature six degrees higher than normal (see Conklin, '12). 

 However, in regard to the last point, it is to be remembered 

 that in modifying the development of eggs a given result can 

 often be produced by several different means. 



There are on the other hand considerations which make it 

 impossible to account for the effects on the basis of temperature 

 changes. Planorbis lays its eggs in shallow water from late winter 

 up into the early summer, and the eggs are adapted to undergo 

 wide changes in temperature without ill effects. They are very 

 small and when the exposures were made were well covered with 

 water in addition to the insulation afforded them by their gelatine 

 and albumen coverings, and furthermore the exposures were of 

 short duration. It is difficult to see, therefore, how sufficient 

 rise in temperature to bring about the marked results herein 

 described could be produced. 



Finally, and this seems to be the test experiment, it cannot 

 be that heating causes the effect, because the X-rays produce 

 the acceleration whether the exposure is longer or shorter. There 

 seems to be no marked difference in the effects of a ten minute 

 exposure and one of three minutes, while one of but twenty 



