1934 ] 
Growth and Determinate Size in Insects 
45 
usually large aquatic insects, and the body-shape of large 
insects is not that which would lessen gravitational stresses. 
We must certainly admit that there is some good reason, 
probably dependent in great part upon the insect’s respira- 
tory and circulatory systems, which acts still more strongly 
to keep its body-size below certain limits. However, as the 
vast majority of insects do not tend to approach these 
limits, such factors are obviously not important ones in reg- 
ulating size as between minute, small or moderate-sized 
forms. We may expect to find correlations between the size 
of the egg or its contained embryo and the size of the 
imaginal insect, and it would be totally unexpected if def- 
inite correlations were not to be found. It is surprising to 
note, however, that such a correlation is by no means uni- 
versal. Many rather large insects, like meloid beetles, pro- 
duce a large number of small or minute eggs, and a survey 
of such cases reveals quite universally some type of develop- 
ment which exposes the early stages to great vicissitudes of 
life. On the other hand some small or minute insects pro- 
duce comparatively very large eggs or young, such as 
certain phorid flies and aphids, and the pupiparous Diptera. 
There are also very striking examples to be found among 
the parasitic tachinid flies where closely similar forms pro- 
duce either many small, or a few large eggs, respectively, 
irrespective of the size of the parent flies. In all such cases 
differences in size at birth are not correlated with imaginal 
size, and represent highly adaptive modifications with re- 
ference to post-embryonic growth which have not in the 
least affected imaginal size. 
Since the primary requirement for growth is food we may 
expect to find size in insects dependent at least to some 
degree upon abundance or type of food. Vegetarian diet 
furnishes a much more constant and plentiful source of food 
materials than that available for forms that depend upon 
animal foods, but larger amounts are necessary to supply 
equal energy. It is very evident in groups where both types 
of food habits occur that the vegetarian forms are more 
numerous in individuals, but do not develop to greater size. 
This is well illustrated by the very populous colonies of 
those ants which subsist on plant food in comparison with 
