224 



SCIENCE. 



[N. S. Vol. XIX. No. 475. 



ations (' mutations ') are in ■ themselves but 

 adaptations of continuous variations, and 

 bearing- always in mind that extreme muta- 

 tions are numerically rare, and, in our present 

 knowledge, obscure as to fate, I take it that 

 we are hardly in a position to give them su- 

 preme importance in the economy of species- 

 building. Of extreme interest they are, none 

 the less, and from theoretical standpoints, they 

 are worthy of the most painstaking research, 

 and are not to be discredited as mere ' freaks ' 

 or ' sports ' important only in the praxis of 

 gardening, as Plate concludes. There is, fur- 

 thermore, a feature of mutations which has, 

 it seems to me, never been adequately con- 

 sidered, i. e., the definiteness of their char- 

 acters, a feature which tells rather in favor 

 of orthogenesis than the less definite in- 

 terpretation which Morgan supports. For 

 in all mutations — we refer to typical cases — 

 the creature which appears is constant to a 

 remarkable degree; the peacock mutant is the 

 black- japanned, never the yellow- nor the red-, 

 and even when many mutants appear ' simul- 

 taneously ' they are surprisingly constant in 

 characters. The word orthogenesis, by the 

 way, does not occur in the index, and in sim- 

 ilar instances we find that the index is trouble- 

 somely brief. 



It is, I conclude, as a postulate of his doc- 

 trine of mutations that Morgan attacks our 

 venerable recapitulation (or, as he prefers to 

 call it, repetition) theory. For when a mutation 

 does occur it appears literally ab ovo, although 

 the author does not commit himself as to the 

 exact point at which the ' presto change ' oc- 

 curred, whether in fertilization or segmenta- 

 tion, but, if I understand him aright, it oc- 

 curred during earliest development; nor does 

 he say concretely whether all mutants date 

 from an identical stage. But the drift of his 

 remarks on recapitulation leads us to infer 

 that they do, for otherwise this chapter seems 

 to lose its point. For, outgrowing the days of 

 Oken, no author of good repute has maintained 

 that the adult structures of ancestors are still 

 present in embryos, nor that the embryo chick 

 resembles an aiult reptile, nor even that the 

 embryo of one species is ever exactly identical 

 with the embryo of the corresponding stage 



of the nearest species. , We .might - even, g<? 

 further and . assert that no modem zoologist 

 has maintained that even within the same 

 species any individual is absolutely identical 

 with any other individual at any correspond- 

 ing stage, early or late, in growth. Even the 

 enthusiast who substituted a cut of an embry- 

 onic dog for one of man, and cheerfully ad- 

 mitted the imposture on the ground that the 

 figures were equivalent, has never been 

 charged with believing that the stages were 

 equivalent, but only with crudely illustrating 

 an elementary text-book, and with unscientific 

 levity. Morgan's therefore must imply some- 

 thing more than the doctrine of von Baer — 

 which was to the effect that chick embryos 

 resemble (he does not say are absolutely iden- 

 tical with) embryos of lizards, and that the 

 stages of chick and lizard correspond during 

 a longer period of development than do em- 

 bryos of chick and fish. And I have gathered 

 what I believe is his meaning only piecemeal, 

 through his references to larval forms, his as- 

 sertion that ' jumps, or short cuts, of the de- 

 velopmental process are unknown in the physi- 

 ological process of development,' and his quo- 

 tations regarding the early appearance of mu- 

 tational characters in the development of birds 

 and dogs. He entirely fails to appreciate, it 

 seems to me, the part played by adaptation at 

 all stages of growth. 



A final word regarding useful variations. 

 Morgan maintains (and we believe that the 

 majority of zoologists are in sympathy with 

 such a view as opposed to Wallace's) that 

 many ' useful ' characters in organisms are 

 useless and accidental, even although, a priori, 

 the case appears adapted to purpose in mar- 

 velous detail. We smile at the silhouetted 

 skull on the back of a moth, or the head of 

 the drowned Taira warrior on the carapace of 

 a Japanese crab, or the profile of a Scandi- 

 navian face on the ' earbone ' of a Norwegian 

 whale, but are these complicated coincidences 

 more accidental than some of the ' purposeful ' 

 variations which we accept rather on the faith 

 of coincidence than upon actual proof of 

 utility? Facts are clearly what we need be- 

 fore we can assert that definite characters or 

 variations are useful — but it is equally true 



