2l8 BIOLOGICAL LECTURES. 



epigenesis surpassed that of Aristotle only in metaphysical 

 extravagance. 1 



That part of Harvey's theory which affirms that the parts of 

 the future organism do not preexist as such, but make their 

 appearance in due order of succession, and which is so often 

 cited as the essence of epigenesis, was all clearly stated by 

 Aristotle. No one, so far as I am aware, now thinks of dis- 

 puting that point. In fact, we are obliged to go much farther 

 than Harvey in this direction, for we cannot say with him that 

 this mode of development holds only of "perfectiora animalia 

 sanguined " (Ex. XLV), but must claim that it is equally true 

 of all those forms he excepted under "metamorphosis." 



The distinction which Harvey made between epigenesis and 

 metamorphosis shows us precisely what he regarded as the 

 most essential thing in generation. To his mind development 

 by epigenesis was the only " proprie dicta generatio" \ and for 

 the reason that it required no preexisting "prepared material'' 

 " Nulla Us immediata materia praeexistens adest " (Ex. XLV, 

 p. 124). The "immaterial conception," the "divine idea," 

 must preexist as " impetum faciens" " Not only is there a 

 soul or vital principle present in the vegetative part, but even, 

 before this there is inherent mind, foresight, and understanding, 

 which from the very commencement to the being and perfect 

 formation of the chick, dispose and order and take up all things 



1 " Let it then be admitted as a matter of certainty," says Harvey, " that the 

 embryo is produced by contagion. But a great difficulty immediately arises, when 

 we ask : In what way is this contagion the author of so great work ? . . . How, 

 I ask, does a nonentity act ? How does a thing which is not in contact fashion 

 another thing like itself? . . . What is it in generation which, in virtue of a mo- 

 mentary contact nay, not even of contact, save through several media forms 

 the parts of the chick from the egg by epigenesis ? " (Ex. XLIX). 



This " contagion " is the calidum innatum, which has its seat in the blood. 

 This is the " vegetative soul, the prime efficient cause of all generation, which 

 moves by no acquired faculty which might be designated by the title of skill or 

 foresight, as in our undertakings ; but operates in conformity with determinate 

 laws like fate or special commandments. ... It is equally manifest that this 

 agent, existing in every egg and seed, is so imbued with the qualities of the parents, 

 that it builds up the offspring in their likeness, not its own." The solution of this 

 grand mystery is found, if we assume " the conception of the uterus to be of the 

 same nature as the conceptions of the brain, and fecundity to be acquired in the 

 same way as knowledge " (Ex. L). 



