240 
are furnished with special muscles, which force the milk into the 
mouths of the young. At first the young are able to use the muscles 
of the mouth only to adhere firmly, but do not possess the strength 
or skill to obtain the milk by sucking. In order to prevent the young 
from being choked, the air passage is entirely separated from the 
throat, and the milk passes on each side of the larynx into the 
oesophagus. After two months have elapsed, the young suck spon 
taneously.”—(See Haeckel, vol. z'., ft. jg/.—Nicholson. Zoology. 
First edition, ft. 627.—Chambers 1 Encycloftaedia—Marsuftialia.) 
I had worked out the problem for myself some years 
ago ; it was therefore very gratifying to find Mr. Romanes, 
when answering Mr. Mivart, giving the same explanation 
of the origin of an instinct which takes effect before the 
intelligence is developed in the higher animals. 
“He (Mr. Mivart) says, ‘it is impossible to believe that any of 
the progenitors of an infant of to-day first acquired, during his or 
her lifetime, the habit of sucking.’ This, no doubt, appears at first 
sight a most conclusive case ; for as the instinct in all mammals 
only lasts during the earliest babyhood of the individual, its incep 
tion can never have been due to intelligence ; while, if its develop 
ment had depended on the slow process of natural selection, all the 
young mammals ought to have been starved before the instinct of suck 
ing had been begun. While writing my own book, this case occurred 
to me as a possible difficulty ; but afterwards I passed it over in view 
of a consideration which must have escaped Mr. Mivart. ‘The pro 
genitors of an infant of to-day’ were the marsupials, and in the 
marsupials the young animal does not suck, or only does so in part; 
it is forcibly fed by the mother, who squirts the milk into its mouth. 
From such a beginning as this, it is easy to understand how the 
instinct of sucking originated, and subsequently became perfected 
in successive generations.”—(Fortnightly Review. vol. xxxviit., 
ftft. 97-8.) 
The case of such instincts does not, therefore, exclude 
intelligence in such a way as to allow for the action of 
Natural Selection to secure the survival of favourable vari 
ations arising among those variations which are incidental 
to birth. For, in the first instance, parental intelligence 
guides the imperfectly developed instincts ; in the second 
case, the instinct is perfect from the first, or very nearly so; 
and the survival of the individual depends upon the