' THE ORIGIN OF SPECIES ' 109 



Embryology, the study of early development in the 

 individual animal or plant, also throws much side light 

 upon the nature and ancestry of each species or family. 

 For example, gorse, which is a member of the pea- 

 flower tribe, has in its adult stage solid, spiny, thorn-like 

 leaves, none of which in the least resemble the foliage 

 of the clover, to which it is closely related ; but the 

 young seedling in its earliest stages has trefoil leaves, 

 which only slowly pass by infinitesimal gradations into 

 flat blades and finally into the familiar defensive 

 prickles. Here, natural selection under stress of 

 herbivorous animals on open heaths and commons has 

 spared only those particular gorse-bushes which varied 

 in the direction of the stiffest and most inedible 

 foliage ; but the young plant in its first days still pre- 

 serves for us the trefoil leaf which it shared originally 

 with a vast group of clover-like congeners. The adult 

 barnacle, once more, presents a certain fallacious ex- 

 ternal resemblance to a mollusk, and was actually so 

 classed even by the penetrating and systematic intellect 

 of Cuvier ; but a glance at the larva shows an instructed 

 eye at once that it is really a shell-making and abnormal 

 crustacean. On a wider scale, the embryos of mammals 

 are at first indistinguishable from those of birds or 

 reptiles ; the feet of lizards, the hoofs of horses, the 

 hands of man, the wings of the bat, the pinions of 

 birds, all arise from the same fundamental shapeless 

 bud, in the same spot of an almost identical embryo. 

 Even the human foetus, at a certain stage of its develop- 

 ment, is provided with gill-slits, which point dimly back 

 to the remote ages when its ancestor was something 

 very like a fish. The embryo is a picture, more or less 



