22 Heredity. 



discovery inaugarated, in. the first half of the last centu- 

 ry, the warm dispute between the Animalculists and the 

 Ovists, one side holding that the germ is contained in 

 the Qgg, and the other that it exists as the seminal ani- 

 malcule. 



It is obvious that, in either form, the evolution theory, 

 as above stated, is logically incomplete, since it only ac- 

 counts for a single generation. Its advocates were there- 

 fore compelled to enlarge it, and to assume that, as each 

 organism thus exists, in a perfect form, in. the preced- 

 ing generation, each germ must contain, on a still smaller 

 scale, the perfect germs of all subsequent generations. 

 Thus Bonnet held, in his hypothesis of emboitement, 

 ^^tliat all living things proceed from pre-existing germs, 

 and that these contain, one inclosed within the other, 

 the germs of all future living things; that nothing 

 really new is produced in the living woi-ld, but that 

 the germs which develop have existed since the beginning 

 of things." (Huxley, Evolution.) 



The advocates of the evolution hypothesis appealed to 

 such facts as the presence of a minute plant inside the 

 acorn, or to the butterfly inside the pupa-skin, in sup- 

 port of their views; but the hypothesis, in its crude state, 

 was quickly overthrown by the first discoveries of mod- 

 ern microscopic embryology. 



Harvey's studies on the development of the chick, 

 followed by the researches of Wolff, Pander, Von Baer, 

 and the host of embryologists of the last fifty years, show 

 conclusivelv that the embrvo is not unfolded out of, but 

 gradually built up from the ^^g. 



We now know that the eggs of all animals, when thoy 

 are not complicated by the presence of food, or of pecul- 

 iar coverings for protection or attachment, are essentially 

 alike in. optical structure, and that they are not only like 



