462 ON GENERATION. 



generation a judgment may be formed of that of all other 

 viviparous animals. Wherefore I shall propose a single genus, 

 by way of general example or type, as we did in the case of the 

 oviparous class ; this made familiar to us, will serve as a light or 

 standard, by means of which all the others may be judged 

 of by analogy. 



The reasons that led me to select the hen's egg as the mea- 

 sure of eggs in general have been already given : eggs are of 

 little price, and are everywhere to be obtained, conditions that 

 permit repeated study, and enable us cheaply and readily to 

 test the truth of statements made by others. 



We have not the same facilities in studying the generation 

 of viviparous animals : we have rarely, if ever, an opportunity 

 of dissecting the human uterus ; and then to enter on the 

 subject experimentally in the horse, ox, sheep, goat, and other 

 cattle, would be attended with immense labour and no small 

 expense; dogs, cats rabbits, and the like, however, will supply 

 those with subjects who are desirous of putting to the test of 

 experiment the matters that are to be delivered by us in this 

 place. 



Fabricius of Aquapendente, as if every conception of a vivi- 

 parous animal were in a certain sense an egg, begins his trea- 

 tise with the egg as the universal example of generation ; and 

 among other reasons for his conclusions assigns this in parti- 

 cular : l " Because the study of the egg has the most exten- 

 sive application, the greater number of animals being engen- 

 dered from eggs." Now we, at the very outset of our observa- 

 tions, asserted that ALL animals were in some sort produced 

 from eggs. For even on the same grounds, and in the same 

 manner and order in which a chick is engendered and deve- 

 loped from an egg, is the embryo of viviparous animals 

 engendered from a pre-existing conception. Generation 

 in both is one and identical in kind : the origin of either is 

 from an egg, or at least from something that by analogy is 

 held to be so. An egg is, as already said, a conception ex- 

 posed beyond the body of the parent, whence the embryo is 

 produced; a conception is an egg remaining within the body 

 of the parent until the foetus has acquired the requisite perfec- 



1 De Form. Ovi et Pulli, cap. 1. 



