Zoology. 435 
gressive diminution, a depopulation of the globe: the two hundred and 
sixty thousand animal and vegetable species which, according to the 
most recent estimations, now cover the surface of the earth, would be 
t the wrecks of a creation infinitely richer in past times. 
he consequence to which the hypotheses of absolute fixity and 
of translation naturally lead: each will judge how far it agrees with the . 
notions that we possess on the ancient condition of the globe. 
(16.) The substitution of the theory of limited variability for the 
hypothesis of absolute fixity renders necessary a new definition of species. 
To approach as nearly as possible the definitions most in use, and for 
the moment, considering only the existing order of things, we shall say : 
ies is a collection or succession of individuals characterized by 
Hybrids are not generally unfruitful, as has often been said ;* they can 
transmit their characters, always mized. Hybrid races are not propa- 
gated with the constancy and regularity observed in species; they soon 
die out, or return by the effect of crossing, to one o the species whence 
they sprung. The transmission is then neither regular nor indefinite. 
It is the same with monstrous or anomalous races. 
Domestic races approach much more nearly to species. Amongst 
create them. The transmission is not then natural. 
2. On some Objects of Natural History from the Collection of Mr. Du 
Chaillu ; by Prof: Owen.—Prof. Owen’s first knowledge of the zoological 
* We have given proofs of this that cannot be refuted, by uniting in two tables 
the indications relative to hybrid Mammifers and Birds, and to their produets, 
