History of the Tlieory of Heredity. 21 



iature chick or germ is made up. Tlie consequence of 

 this intnssnsecptive growth is the '^development" or 

 *^ evolution" of this germ into the visible bird. Thus 

 an organized individual *^is a composite body consisting 

 of the original or elementary parts, and of the matters 

 which have been associated with tliem by the aid of nu- 

 trition," so that if these matters could be extracted from 

 the individual, it would, so to speak, become concentra- 

 ted in a point, and would thus be restored to its primi- 

 tive condition of a germ ^^ just as by extracting from a 

 bone the calcareous substance which is the source of its 

 hardness it is reduced to its primitive state of gristle 

 and membrane." 



** Evolution and development are, for Bonnet, sy- 

 nonymous terms; and since, by evolution he means 

 simply the expansion of that which was invisible into 

 visibility, he was naturally led to the conclusion, at 

 which Leibnitz had arrived by a different line of reason- 

 ing, that no such thing as generation exists in nature. 

 The growth of an organism being simply a process of 

 enlargement, as a particle of dry gelatine may swell up 

 by the intussusception of water, its death is a shrinkage, 

 such as the melted jelly might undergo on desiccation." 



Much more anciently the evolution hypothesis found 

 acceptance in a somewhat different form, and the minia- 

 ture organism was believed to exist in the male element, 

 and to receive from the egg the nourishment needed for 

 its growth and perfect development. 



Leeuwenhoek's discovery of the motile spermatozoa of 

 animals was regarded as a new basis for this view, and 

 the ^^sperm-animalcule" was held to be the perfect and 

 living animal ready for unfolding or evolution, the term 

 ''spermatozoon," still retained in scientific nomenclature, 

 being a remnant of this old hypothesis. Leeuwenhoek's 



