■go PRIMITIVE FORMS OF LIFE 



Recent researches, moreover, have shown that the action 

 of radiation on organic compounds is often reversible, and 

 E. Bourquelot and Bridel have demonstrated that in the 

 same way ferments are generally able, under certain con- 

 ditions, to reconstruct what they have destroyed. 1 It 

 would seem that we may attribute heredity to a similar 

 reversibility. This statement is not, of course, an ex- 

 planation of the phenomena of heredity, but it does permit 

 us to get a glimpse of how these phenomena arose ; opens 

 the way to accurate research, and allows us from the outset 

 to eliminate as useless those hypotheses which demand almost 

 supernatural, or, at least, intangible agencies. Yves Delage, 

 in his book on Heredity, entered into a learned discussion of all 

 these questions, which will probably be solved only by 

 extremely minute investigations in the bio-chemical laboratory. 

 However that may be, if we consider heredity with regard 

 to its effects and not its causes, we shall all agree in attributing 

 to it the function of maintaining, in the lineage of organisms, 

 the characters acquired under the influence of determined 

 causes after these causes have themselves ceased to act. At 

 first sight, consequently, it would appear to be an essentially 

 conservative force, but for this very reason it creates the gravest 

 difficulties for all investigations into the causes determining 

 the characters of living beings, simply because heredity main- 

 tains these characters under conditions manifestly incapable 

 of producing them, and with which they may even be com- 

 pletely out of harmony. But that is not all : even when these 

 organisms continue to live under the conditions which have 

 determined their characters, the characters appear when the 

 causes are incapable of acting as, for instance, during 

 embryonic life ; or, if the characters are periodic, they may 

 occur out of their appropriate season. Thus it happens that the 

 correspondence between the journeys of migratory birds and 

 variations in temperature is relative only. Accustomed as 

 naturalists are to observe organic characters and embryonic 

 phenomena generally without finding it possible to trace them 

 back to definite external causes, and powerless as they are to 

 give irrefutable proof of the existence of any causes they may 

 suspect, they have ceased to be interested in the search for 

 any explanation, and have declared this search to be vain, if 



1 LXVII, 63. 



