^ BIOLOGICAL THEORIES. 587 



Z092. 



It was the facility for explaining this phenomenon offered by the 

 theory I have set forth which first led me, in fact, to believe in my 

 own speculation. Pangenesis always has appeared to me impossible, 

 and " perigenesis " absurd, while " continuity " never appeared to 

 explain the ordinary phenomena, even if such a continuity had been 

 demonstrated to be universal. My own theory appeared merely 

 plausible till consideration of the Termites made it credible. 



Hitherto advantageous characters and disadvantageous characters 

 have been referred to, and though I have not explicitly stated that 

 adult characters are meant, I fear that, unless I emphasise the 

 opposite of that interpretation, I may be understood to refer to such 

 characters alone. Such an interpretation is by no means intended. 

 When I speak of characters advantageous to the individual, the 

 characters I really mean are the whole series of characters from 

 the very earliest stage in the production of an ovarian cell to the very 

 last moment of life. The favoured stock-constitution is the one 

 which leads to the formation of those new individuals which through- 

 out the whole course of their existence are on the average best 

 fitted for competition at each successive stage. Just as I have insisted 

 on the more or less independent estabUshment of each character of 

 the individual, so I would now insist on the more or less independent 

 establishment of every character, not only of the adult, but of the 

 individual at every successive stage of development. 



There are animals — some LepidopUra for instance — in which the 

 most striking characteristic of the larvae is their variety, and yet the 

 variation among the adults is so slight as almost to defy detection. 

 If variation in those characters of the stock-constitution which deter- 

 mine the external characters of the larvae be not disadvantageous 

 to the species, natural selection will have no power to hniit that 

 variation, although it may impose the narrowest limitation upon the 

 variation of that same constitution so far as the external characters 

 of the adult are concerned. The only variations in the larvae which 

 natural selection can limit in extent or in frequency are those which 

 are disadvantageous to the species as a whole. 



The form of a caterpillar or of a naupHus is as strictly determined 

 as that of the adult, probably even more strictly. If the efficiency of 

 natural selection is proportional to the intensity of the struggle for 

 existence, then it would seem strange if the stages in which most indi- 

 viduals die should be least affected by that selection. For every adult 

 Peneus which dies without contributing to the multiplication of its kind, 

 it is probably no exaggeration to say that a thousand succumb to the 

 pressure of external circumstances in the " nauplius " phase. The 

 characters of the nauplius I hold to be determined in the same way 

 as those of the adult, and the "inheritance" of larval characters I 

 claim to be expHcable by the 'theory I have advanced for the 



explanation of " heredity'" in general. 



C. Herbert Hurst. 



