SOME STRANGE NURSING HABITS 
Wuite the instinct of taking care of their progeny, whether 
these are born in the living stage or first come into the 
world in the form of eggs, is more or less deeply 
implanted in the higher vertebrates, among the lower 
members of that great group the eggs and young are 
very frequently left to shift for themselves. Still this 
state of things is by no means universally the case; and 
I shall show in the course of the present article that 
certain amphibians and fishes exhibit structural modifica- 
tions for the purpose of protecting their eggs and young, 
which are almost or quite unparalleled elsewhere. Cele- 
brated as they mostly are on account of their highly 
developed parental instincts, birds exhibit no instances 
where the body of either parent is specially modified 
for the purpose of carrying about either the young or 
the eggs after their extrusion. And I believe that the 
same holds good with regard to reptiles, although into 
the disputed question whether vipers afford protection to 
their young by allowing them to run down their throats 
I am not going to enter here, beyond confessing that I 
am inclined to trust the numerous observers who state 
that they have seen the phenomenon with their own eyes. 
With certain groups of mammals—notably the marsupials 
—the case is, however, different, many of them, like the 
kangaroos, carrying their imperfectly developed young in 
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