1884] Growth, its Conditions and Variations. 1087 
readily. Other elements than mere nutrition enter into the prob- 
lem, and its full consideration requires a review of all the condi- 
tions of organic life. 
As we ascend in the scale of life we find animals to be pos- 
sessed of constantly more efficient food-taking organs. From 
the cilia of the Infusoria and the Sponges we pass to the Ccelen- 
terate tentacles and thread cells, the sucking disks of the Cephal- 
opoda, the pincers of the Crustacea, and the limbs and teeth of 
the Vertebrata, with numberless intermediate implements of cap- 
ture. There is a like range of efficiency in the weapons of each 
sub-kingdom and class of animals. An Octopus, for instance, is 
a thousand fold more efficiently armed than an oyster, and a man 
thanamouse. There is a like variation in the rapidity of motion 
of various animals, some being completely sedentary, others ex- 
ceedingly active. Their mental powers vary in like manner, from 
utter obtuseness to great quickness of intellect. 
All these differences enter into the question of difference of size, 
yet they only partly suffice to solve the problem. Great diver- 
sity occurs between animals of equal organic efficiency, muscular 
activity and mental quickness. A rat, indeed, is superior in all 
these requisites to a cow or a hippopotamus, and a mouse is cer- 
tainly a more highly organized animal than a whale. It has 
more efficient and better armed limbs, a greater variety of move- 
ments and diversity of habits, and probably superior mentality. 
In this latter respect, however, the ant is in advance of many 
Massive vertebrates, yet it remains one of the smallest of its own 
class of insects, the largest of which are certainly not the 
shrewdest, 
: If we take a close survey of the animal kingdom, one interest- 
ing fact quickly appears, namely, that all the animals below man 
exist but for three purposes, to obtain food, to escape danger and 
to reproduce their kind. No other marked purpose in their lives 
can be seen. They rest and sleep to regain strength, they occa- 
sionally employ their excess vigor in play, and curiosity and 
imitation are now and then displayed, but only strongly in the 
Monkey tribe, Yet the great purposes of their lives, and of 
lower man as well, are the three above named. Only in higher 
man do the faculties of curiosity and imitation unfold into the 
desire for knowledge, and the designed effort to attain advanced 
conditions, which are the basic principles of the higher mental 
