INDIVIDUALITY AND HYBRIDITY. 657, 
of free motion and of maintaining an independent existence. 
So with many other Colenterates and with the tapeworm, 
whose proglottides or segments are finally capable of sepa- 
rate existence. Among the higher invertebrates, even the 
different members of a colony of white or true ants lack a 
certain amount of individuality, the workers performing 
labors upon which the maintenance of the very existence of 
the colony depends, so that there are different grades of in- 
dividuality, from examples like the Hydractinia and the 
Siphonophores up to those insects which live socially ; and 
we see that the most perfect individuality exists in those 
animals which can most efficiently provide for their own 
sustenance and for the continuance of their species. 
Hybridity.—It is rare that two species, even of the same 
genus, can produce offspring ; when such cases occur. the 
result is called a hybrid. For example, the mule is a hybrid, 
being bred from a female horse and an ass; but the mule 
is not fertile, and hybrids are very rarely fertile. The In- 
dian dog and coyote are said by Coues to interbreed, and 
on the Upper Missouri we have seen dogs which had every 
appearance of being such hybrids. Dogs also cross with the 
fox (Darwin). The American bison is known to breed with 
the domestic cattle, and it seems to be a well-established 
fact that the hybrids are fertile. Fish readily hybridize. 
Darwin states that he knows of no thoroughly well-au- 
thenticated cases of perfectly fertile hybrid animals, though 
he adds, ‘‘I have reason to believe that the hybrids from 
Cervulus vaginalis and Reevesit and from Phasianus col- 
chicus with P. torquatus are perfectly fertile.’’ The hare 
and rabbit are supposed to have fertile offspring ; the hy- 
brids of the common and Chinese geese (Anser cygnoides) 
are fertile. The crossed offspring from the Indian humped 
and common cattle interbreed. Caton has hybridized the 
Virginia deer with the Ceylon deer and the Acapulco deer ; 
“the hybrids seem perfectly healthy and prolific.” Among 
insects over 100 cases of hybridity have occurred. Hybrids 
between the brown and polar bear, the leopard and jaguar, 
Equus onager and EL. hemippus, E. burchelli with the com- 
mon horse, and with the common ass and &. hemionus : 
have been raised. 
