6 The Recapitulation Theory and Human Infancy 



stage is a true snail; it has gills which hang free at the sides of 

 the body as is the case in Unio pictorum. It has even a byssus, 

 as in Mytilus, in order to cling to the grass. The tail is nothing 

 else than the foot of the snail. The metamorphosis of an insect 

 is a repetition of the whole class, scolopendra, oniscus, julus, 

 spider, crab." 2 



Later, in 1883, Oken wrote, in reference to the same matter, 



"There is no doubt that we have here a striking resemblance, 

 and one that justifies us hi thinking that the development in 

 the ovum is merely a repetition of the story of the creation of 

 the animal groups." 3 



Here, plainly enough, is a statement in crude form of the idea 

 of recapitulation which was to have clear definition with the 

 advent of the doctrine of descent, and which was destined to 

 play so important a role in the history of that doctrine. 



The other early references to be noted make comparisons 

 of development with the rank of existing animals. Thus, Wal- 

 ther, in 1808, said, 



"The human foetus passes through its metamorphosis in the 

 cavity of the uterus in such a way that it repeats all classes of 

 animals, but, remaining permanently in none, develops more 

 and more into the innate human form. First the embryo has 

 the form of a worm. It reaches the insect stage just before its 

 metamorphosis. The origin of the liver, the appearance of the 

 different secretions, etc., show clearly an advance from the 

 class of the worm into that of the mollusk." 4 



The embryologist Meckel, in 1808, 1811, and 1821, gave 

 greater definiteness to these comparisons: 



"He held that the embryo of higher forms, before reaching 

 its complete development, passes through many stages that 

 correspond to those at which the lower animals appeared to be 

 checked through their whole life. In fact the embryos of higher 

 animals, the mammals, and especially man, correspond in the 

 form of their organs, in their number, position, and proportionate 

 size, to those of the animals standing below them. The skin is 

 at first, and for a considerable period of embryonic life, soft, 

 smooth, hairless, as in the zoophytes, medusae, many worms, 

 mollusks, fishes, and even in the lower amphibians." 6 



' Quoted by Morgan, Evolution and Adaptation, 1903, p. 59. 

 Quoted by Bolsche, Haeckel, His Life and Works, translated by J. McCabe, p. 

 227. 



Quoted by Morgan, loc. cit., p. 59. 

 ZWd. 



