FUNDAMENTAL RELATIONS OF ANIMALS 13 



from the affinities or the anatomical structure of animals, or from 

 their habits and their geographical distribution, from their em- 

 bryology, or from their succession in past geological ages, and the 

 peculiarities they have exhibited during each,^^ believing as I do 

 that isolated and disconnected facts are of little consequence in the 

 contemplation of the whole plan of creation; and that without a con- 

 sideration of all the facts furnished by the study of the habits of 

 animals, by their anatomy, their embryology, and the history of the 

 past ages of our globe, we shall never arrive at the knowledge of the 

 natural system of animals. 



Let us now consider some of these topics more specially. 



SECTION II 



SIMULTANEOUS EXISTENCE OF THE MOST DIVERSIFIED TYPES 

 UNDER IDENTICAL CIRCUMSTANCES 



It is a fact which seems to be entirely overlooked by those who 

 assume an extensive influence of physical causes upon the very ex- 

 istence of organized beings that the most diversified types of animals 

 and plants are everywhere found under identical circumstances. The 

 smallest sheet of fresh water, every point upon the seashore, every 

 acre of dry land teems with a variety of animals and plants. The 

 narrower the boundaries are which may be assigned as the primitive 

 home of all these beings, the more uniform must be the conditions 

 under which they are assumed to have originated; so uniform, in- 

 deed, that in the end the inference would be that the same physical 

 causes could produce the most diversified effects. ^^ To concede, on 



" Many points little investigated thus far by most naturalists, but to which I have 

 of late years paid particular attention, are here presented only in an aphoristic form, 

 as results established by extensive investigations, though unpublished, most of which 

 will be fully illustrated in my following volumes, or in a special work upon the plan 

 of the creation. (See Agassiz, "On the Difference between Progressive, Embryonic, and 

 Prophetic Types in the Succession of Organized Beings," Proceedings, American Asso- 

 ciation for the Advancement of Science, II (1850), 432-438. 



^* In order fully to appreciate the difficulty alluded to here, it is only necessary to 

 remember how complicated and at the same time how localized the conditions are 

 under which animals multiply. The egg originates in a special organ, the ovary; it 

 grows there to a certain size, until it requires fecundation, that is, the influence of 

 another living being, or at least of the product of another organ, the spermary, to 

 determine the further development of the germ, which, under the most diversified 



