THE PRINCIPLES OF BIOLOGY. 
311 
chickens. “ Equally clear proof that abundant nutriment 
raises the rate of multiplication, occurs among Mammals.” 
Comparisons of the litters of the dog with those of the wolf 
and fox are shown to be considerably in favour of the dog. 
So with the wild and tame cats. So with the stoat and 
ferret. “ Perhaps the most striking contrast is between the 
wild and tame varieties of the pig.” While the one produces 
according to its age from four to ten young ones once a year, 
the other produces sometimes seventeen in a litter, or will 
bring up five litters of ten each in two years—“ a rate of 
reproduction that is unparalelled in animals of as large a 
size, and it is specially noted “ that this excessive fertility occurs 
where there is the greatest inactivity—where there is plenty 
to eat and nothing to do.” * * * 
The remainder of the chapter is devoted to meeting an 
objection :—“ Many facts may be brought to prove that 
fatness is not accompanied by fertility, but by barrenness; 
and the inference drawn is that high feeding is unfavourable 
to genesis. The premiss may be admitted, while the con¬ 
clusion is denied.” * * * 
The following chapter (X.) shows (1) that “if certain 
organisms are so circumstanced that highly nutritive matter 
is supplied to them without stint, and they have nothing to do 
but absorb it, we may infer that their powers of propagation 
will be enormous. If there are classes of creatures that 
expend very little for self-support in comparison with allied 
creatures, a relatively extreme prolificness may be expected of 
them. (2) Or if, again, we find species presenting the 
peculiarity that, while some of their individuals have much 
to do and little to eat, others of their individuals have much 
to eat and little to do, we may look for great fertility in these 
last, and comparative infertility, or barrenness, in the first.” 
The numerous illustrations which follow amply verify these 
anticipations. A few only are selected :—(1) Parasitic plants 
like the UajfiesiacecB, which live on the juices they absorb from 
other plants, have their organs for self-support only rudi¬ 
mentary because needless, but the organs devoted to repro¬ 
duction, and distribution of germs, constitute the mass. 
Fungi, which grow on living plants, have the spore-producing 
parts relatively enormous. Parasitic animals, both in the 
Epizoa and Entozoa, afford similar illustrations, especially so 
in the nematoid Entozoa , where the mature female of Ascaris 
lumbricoid.es, living in the body of its host, and surrounded by 
nutriment, contains, according to Eschricht, as many as 
04,000,000 ova, and even this remarkable number is exceeded 
among the cestoid Entozoa. The phenomena of pseudo- 
