286 ANNUAL OF SCIENTIFIC DISCOVERY. 



of the air, and the lime, soda, phosphorus, potash, water, etc., from the 

 earth, come together, and on the instant combine into a completely 

 formed horse, lion, elephant* or other animal V If this question is an- 

 swered in the affirmative, it will be easily seen that the answer is en- 

 tirely opposed by the observed analogies of nature. In the practical 

 study of the history of the earth and the changes which it has under- 

 gone, of the development of individual animals and plants, the " order 

 of nature " points in one direction, namely, to the process of different- 

 iation. The one-celled plant and the tree, the polyp and man, and all 

 organic forms intermediate between these extremes, pass from the 

 homogeneous to the heterogeneous, from the nucleated cell, or even 

 from what is more simple still, from plasma to the adult individual con- 

 sisting of organs more or less complex, according to the position in the 

 series. We nowhere see plants or animals reach maturity in any other 

 way than by development or growth. 



At the same time, we must not lose sight of the fact that what is 

 true of the successive stages of individual organisms may not necessa- 

 rily prove true with regard to the history of the races ; that while, from 

 the earliest embryonic condition of each individual to the last there is 

 a connected series of observed changes or differentiations, and no break 

 in the organic continuity, there are no observations whatever to prove 

 a like organic continuity in the races. In the absence of such direct 

 proof, we have no other alternative than to look to the analogies of 

 nature and the geological record. The direction in which the former 

 point is obvious ; the testimony of the latter is thus far negative, but is 

 it complete enough to be a safe guide ? 



In view of the difficulties met with, in explaining the first introduc- 

 tion of living forms, Agassiz has put forth the hypothesis of the creation 

 of eggs. " I then would ask, is it probable that the circumstances un- 

 der which animals and plants originated for the first time can be much 

 simpler, or even as simple as the conditions necessary for their repro- 

 duction only, after they have .been once created ? Preliminary then 

 to their first appearance, conditions necessary for their growth must 

 have been provided for ; for, if, as I believe, they were created as eggs, 

 the conditions must have been conformable to those in which the living 

 representatives first introduced now reproduce themselves. If it were 

 observed that they originated in a more advanced stage of life, the dif- 

 ficulty would be still greater, as a moment's consideration cannot fail 

 to show, especially if it is remembered how complicated the structure 

 of some of the animals was, who are known to have been among the 

 first inhabitants of our globe." Contrib. Nat. Hist, of U. States, 1. 12. 



This hypothesis would answer very well for spawning fishes and rep- 

 tiles, whose eggs may be trusted to the effects of physical agents. But 

 does it help us with regard to viviparous reptiles and mammals ? To 

 take the case of the mammals, what " conditions conformable to those 

 in which the living representatives first introduced now reproduce 

 themselves " would answer the purpose for the development of the 

 young, except a uterus, or something analogous to a uterus, and for 

 its nourishment after birth, except a mammary gland, or something 

 analogous to one V And how could there be a uterus or a mammary 

 gland without organs of nourishment, locomotion, etc. ; in other words, 

 before creating the egg, it would be necessary to create some kind of 



