Growth, its Conditions and Variations. 1099 
domestic dog, for instance, a remarkable diversity has been in 
this way produced. The same effect, though less marked, ap- 
pears in the other domestic animals. It has become strikingly 
produced in the horse without design, but merely through diver- 
sity in quantity of food, and in the necessary exertion to obtain 
it in different localities. In these instances we recognize the in- 
fluence of heredity in preserving variations of chance occurrence. 
It may be remarked here that man is not the only animal which 
practices intelligent selection. Bees and ants pursue the same 
process with their own young, and with remarkable results. Thus 
with the hive bee a special feeding of one of the worker larve 
Yields not only increased size but an important organic develop- 
ment. From being a sterile worker it becomes a functional 
female, or queen. In the ants the sterile forms often differ widely 
in size. Dr. McCook measured in one nest nine distinct sizes, 
the largest being seven times the length of the smallest. Whether 
this is a result of designed difference of nutrition of the larve 
does not appear, though there are two or three distinct duties in 
the nest to which ants of distinct sizes apply themselves. 
But we have now to consider another phase of the subject 
which has been of extreme importance in its history. In addi- 
tion to the influences whose effect upon the sizes of animals we 
have considered, there is another of equal, if not greater, efficacy. 
€ look upon the tentacle as a weapon of minor power, yet in 
the cuttle-fish it has become an exceedingly powerful instrument, 
and through its aid giant animals have been produced. The same 
may be said of the weapons of the Crustacea, which sufficed, in 
an early geological period, to yield crustaceans of six feet in 
Even the Medusæ, with their apparently feeble food- 
taking powers, occasionally attain to great bulk. They are per- 
haps situated like the whale in the midst of an abundant supply 
Pi defenceless food, which can be obtained without special exer- 
ion. The defenceless prey of these great sluggish animals are 
those small creatures which trust to’excessive reproductive pow- 
aa for continuance of their race, and thus have less need of effi- 
cent personal defence than with the less prolific. 
These cases point to the condition now to be reviewed, that of 
comparative ability to share in the limited food supply. The 
le for existence is by no means confined. to the power of 
attack and defence, but also takes the form of a struggle to obtain 
