310 
THE PRINCIPLES OE BIOLOGY. 
environment as bring a larger supply of the materials or forces 
on which both parental life and the lives of offspring depend. 
Be there, or be there not, any expenditure, a higher nutrition 
will make possible a greater propagation. We may expect 
this to hold both of agamogenesis and of gamogenesis; and 
we shall find that it does so.” 
The following illustrations, which are given mostly in 
Mr. Spencer’s own words, will be appreciated by every 
naturalist. 
44 On multi-axial plants, the primary effect of surplus 
nutriment is a production of large and numerous leaf-shoots. 
How this asexual multiplication results from excessive 
nutrition is well shown when the leading axis, or a chief 
branch, is broken off towards its extremity. The axillary 
buds below the breakage quickly swell and burst into lateral 
shoots, which often put forth secondary shoots : two gener¬ 
ations of organic individuals arise where there probably would 
have been none but for the local abundance of sap, no longer 
drawn off.” 
“No less conclusive is the evidence furnished by agamo¬ 
genesis in animals.” Sir John Dalyell, speaking of Hydra 
tuba , on which he had made some original observations, 
remarked: — “It is singular how much propagation is 
promoted by abundant sustenance. This polype goes on 
budding-out young polypes from its sides with a rapidity 
proportionate to the supply of materials.” * * * 
It is further shown that “ the sexual multiplication of 
organisms under changed conditions, undergoes variations 
conforming to a parallel law. Cultivated plants and domes¬ 
ticated animals yield us proof of this.” 
Omitting for the sake of brevity the illustrations as to 
plants, those of animals are given, more particularly as to 
Birds and Mammals. In birds, “ let us first contrast the 
farm-yard Gallinacea with their kindred of the fields and 
woods. Notwithstanding their greater size, which, other 
things equal, should be accompanied by smaller fertility, the 
domesticated kinds have more numerous offspring than the 
wild kinds. A turkey has twelve in a brood, while a pheasant 
has from six to ten. Twice or thrice in a season a hen rears 
as many chickens as a partridge rears once in a season.” 
“ Anserine birds show us parallel differences.” Tame geese 
and ducks not only lay a larger number of eggs, and rear 
more young than wild ones, but the eggs are of larger size. 
So with pigeons. Every experienced poultry-keeper knows 
that to secure a good supply of eggs his fowls must be kept 
well fed and well housed. The same holds good as to rearing 
