The History of Biology 383 



Schultze (1825-1874) in the early sixties established the idea of pro- 

 toplasm as the living substance of all cells. This protoplasm was called 

 by Huxley the "physical basis of life." 



In embryology Fabricius (1537-1619) published a paper describing 

 the sequences of development in the hen's egg up to the time of hatching. 

 Harvey was a pupil of Fabricius, and built upon the work of his master. 

 These men opposed the pre-formationists, and called their theory 

 epigenesis — which simply means that the embryo arises by a gradual 

 differentiation of unformed material in the egg. 



Malpighi in 1672 sent two important papers on embryology to the 

 Royal Society, but apparently the time was not yet ripe for his work 

 and it was neglected for nearly a century. He stood with the epigenetic 

 group. 



Bonnet (1720-1793) was one of the important men at this time who 

 threw the weight of his influence with Haller toward the pre- 

 formationists. 



At present embryologists hold, as was stated above, that there 

 really is an organization of some kind in both egg and sperm, but that 

 no embryonic shape has yet been established. The definite shape comes 

 forth only by the gradual differentiation of the unformed (but not 

 unorganized) matter. We may, therefore, say that "the whole future 

 organism is potentially and materially implicit in the fertilized egg cell," 

 which means that both sides were partially right. 



However, the greatest name in embryology is von Baer (1792-1876). 

 His work was done in the thirties of the last century. He is the father 

 of comparative embryology. It was he who first noted and described 

 cleavage, germ-layers, tissue, and organ differentiation, and gave us the 

 well-known "recapitulation theory," now often called Haeckel's "Law of 

 Biogenesis," on account of Haeckel's popularization of it. It will be 

 remembered that this theory holds that embryos pass through the adult 

 stages of the race to which they belong. 



The origin of life has always been an interesting speculative subject 

 for thinking men, and many and mysterious are the ways in which life 

 was supposed to spring forth spontaneously. Aristotle thought that 

 mice developed from the river's mud, while later writers suggested that 

 old rags and cheese combined in a dark cellar would produce the same 

 result. The history of this subject makes more than fascinating reading. 



Francesco Redi (1626-1698) was probably the first man to demon- 

 strate experimentally that life did not spring forth spontaneously as 

 commonly supposed. He placed very thin cloth over a dish containing 

 decaying meat and found tliLt, when flies were thus prevented from 

 coming in contact with the meat, no maggots formed, although maggots 

 were always supposed to arise spontaneously from decaying meat. But 

 Redi himself found parasites of various kinds within the bodies of other 



