152 
ANIMAL PEDIGREES. 
July, 1891. 
length it becomes solid and remains so until a length of about 
\ inch has been attained. The solidification occurs at a 
stage closely corresponding with that in which it first appears 
in the dogfish, and a curious point about it is that in the frog 
the oesophagus becomes solid just before the mouth opening 
is formed, and remains solid for some little time after this 
important event. 
This closing of the oesophagus clearly cannot be recapitu¬ 
lation, but the fact that it occurs at corresponding periods in 
the frog and the dogfish suggests that it may possibly, as 
Balfour hinted, “ turn out to have some unsuspected morpho¬ 
logical bearing.” 
A matter which at present is attracting much attention is 
the question of degeneration. 
Natural selection, though consistent with and capable of 
leading to steady upward progress and improvement, by no 
means involves such progress as a necessary consequence. 
All it says is that those animals will, in each generation, 
have the best chance of survival which are most in harmony 
with their environment, and such animals will not necessarily 
be those which are ideally the best or most perfect. 
If you go into a shop to purchase an umbrella the one you 
select is by no means necessarily that which most nearly 
approaches ideal perfection, but the one which best hits off 
the mean between your idea of what an umbrella should be 
and the amount of money you are prepared to give for it ; 
the one, in fact, that is on the whole best suited to the cir¬ 
cumstances of the case, or the environment for the time being. 
It might well happen that you had a violent antipathy to a 
crooked handle, or else were determined to have a catch of a 
particular kind to secure the ribs, and this might lead to the 
selection, i.e., the survival, of an article that in other and 
even in more important respects was manifestly inferior to the 
average. 
So is it also with animals: the survival of a form that is 
ideally inferior is very possible. To animals living in pro¬ 
found darkness the possession of eyes is of no advantage, 
and forms devoid of eyes would not merely lose nothing 
thereby, but would actually gain, inasmuch as they would 
escape the dangers that might arise from injury to a delicate 
and complicated organ. In extreme cases, as in animals lead¬ 
ing a parasitic existence, the conditions of life may be such 
as to render locomotor, digestive, sensory, and other organs 
entirely useless; and in such cases those forms will be most 
in harmony with their surroundings which avoid the waste 
of energy resulting from the formation and maintenance of 
these organs. 
(To be continued.) 
