BOTANY. 



The Law of Embryonic Development in Animals and Plants. 

 — An article upon this subject in the American Naturalist for 

 May contains a hasty generalization, based upon pure assump- 

 tion, or upon insufficient data, and supported only by a false anal- 

 ogy. It opens with the startling proposition that "it is a well 

 known law in the animal kingdom, that the young or embryonic 

 state of the higher orders of animals resemble (sic) the full-grown 

 animals of the lower orders." If such a law had ever been dis- 

 covered to exist, the tadpole and the caterpillar, which are cited 

 in proof, would certainly be good illustrations of it. But this 



the causes of the recent rapid progress in the study of the animal 

 kingdom," that no eminent living naturalist or biologist recognizes 

 the existence of such a law ; or at least no one of them gives a 

 hint of it in his writings. 



Agassiz claimed that ancient animals resembled the embryos of 

 recent animals of the same class, and that the geological succes- 

 sion of extinct forms is parallel with the embryological develop- 

 ment of existing forms. But if this principle* be true, it is far 

 from meeting the requirements of the "law" of this article. 



The writer of it may have had in his mind a vague idea of the 

 law of Von Baer, which is well known, and which has enabled nat- 

 uralists " to correct their systems of classification," viz. : " That, 

 in its earliest stages, every organism has the greatest number of 

 characters in common with all other organisms, in their earliest 

 stages." Or, to put it in language parallel to that of the "law" 

 of this article, false syntax excepted ; the embryonic state of the 

 higher orders of animals resembles the embryonic (not the full 

 grown) state of the lower orders. The germ of a human being 

 differs in no visible respect from the germ of every animal and 

 plant : it never resembles any full grown animal or plant. It suc- 

 cessively looses its resemblance to vegetable embryos, then to all 

 embryos but those of Vertebrates, then to all but those of Mam- 

 mals. Finally it resembles only the embryos of its own order, 

 Primates ; and at birth the infant is like the infants of all human 

 races. 1 But never at any period of its successive differentiations 



isee Spencer's Biology, VoM. ~ 



