842 
PROGRESS OF ZOOLOGY. 
hare and the rabbit, and with each other. Some of these 
leporines have borne young in the gardens of the Zoological 
Society, but whether they are of the first cross is at present 
unknown. The differences between the two types are many, 
yet they are rather in degree than kind. The heart of the 
hare is nearly five times the weight of that of the rabbit, the 
lungs are nearly four times as heavy, the calibre of the tra¬ 
chea three or four times as great. Furthermore, the period 
of gestation in the hare is understood to be a month, that of 
the wild rabbit three weeks ; the young of the rabbit are born 
blind, those of the hare see; the rabbit burrows, the hare 
seldom goes to earth. There is one great peculiarity of these 
hybrids of very great importance as to the question at issue— 
the males show a great disinclination to copulation, which is 
very different to the males of the (so-called) species, and if 
we were to suppose such a cross to arise in nature, we must 
also suppose it would soon be lost through this very pecu¬ 
liarity. But much more interesting cases, bearing on the 
same question, were commuhicated by Dr. Crisp, in the paper 
from which we have gathered the above particulars. # Four 
hybrid ducks were bred at the Zoological Gardens between 
the summer duck (Anas sponsa) , the pochard (Fuligula ferina ), 
and the ferruginous duck (Fuligula nyroca ). It is true that 
in these instances the parent species are in structure and 
habits very nearly allied, and the only difference of importance 
is that the summer duck has eight pairs of ribs, the others 
have nine; but an extra pair of ribs is no proof of specific 
distinctness, for in man an extra pair occurs occasionally, 
and in the anthropoid apes there is sometimes a pair of ribs 
and one or two vertebrae above the typical number, and the 
ribs themselves are but elongations of processes with which 
every segment of the vertebral column is furnished. But 
these facts compel us to ask, still more eagerly, what is a 
species? Are the three species of duck just named specifi¬ 
cally identical, and did the hare and the rabbit originally 
proceed from the same stock ? 
(To be continued .) 
# Proceedings of Zoological Society , Feb. 12, 1861, paper bv Edward 
Crisp, M.D., E.L.S. 
