CHLOÉON (EPHEMERA) DIMIDIATUM. 65 
altogether absent; neither the Actinozoa nor the Echinodermata have a single freshwater 
representative. 
But while so many families are absent, their places are not left unoccupied. Not 
only do the insects themselves in a great measure restore the balance, but their larvæ 
also do much to relieve the monotony. Many situations are thus filled; much food is 
thus perhaps made available which would not otherwise contribute towards the support 
of animal life. 
Insects, indeed, are not the only animals which undergo metamorphoses even after 
birth; every subkingdom supplies some instance. In this manner perhaps the world 
supports more life, and the sum of happiness is therefore greater, than would be the case 
if every creature arrived at its perfect form before quitting the egg. 
I have still used the old word “larva” to denote the first part of the life of an insect 
after birth. If, however, there is any truth in the preceding observations, it is evident 
that the so-called “larva ” of a Fly corresponds properly neither with that of a Moth nor 
with that of a Grasshopper, and it is always inconvenient to use one word with several 
meanings. Much of the confusion in political economy has arisen from the unfortunate 
use of the word * money " to mean either capital in general or the circulating medium in 
particular. 
And yet it would be very difficult to remedy the inconvenience in the case of the word 
“larva.” Not only is it almost necessary for entomology that there should be one word to 
denote the early stages in the life of an insect, but it would be perhaps impossible to give 
the word a more definite meaning without restraining it within very narrow limits. In 
fact, insects leave the egg in every possible stage of development. The maggots of 
Flies, in which the appendages of the head are rudimentary, belong to a lower grade 
than the grubs of Bees, &e., which have antennz, mandibles, and maxille, labrum, 
labium, and, in fact, all the mouth-parts of a perfect insect. 
The caterpillars of Lepidoptera are generally mentioned with the larvee of Diptera and 
Hymenoptera, and placed in opposition to those of Orthoptera, Hemiptera, &c. But, in 
truth, the possession of thoracic legs places them, as well as the similar larvae of the 
Tenthredinidee, on a decidedly higher level, while in the development of the cephalic 
appendages there is, as already mentioned, a marked difference between the maggots of 
Flies and the grubs of Bees. : init 
Thus then the period of growth (that in which the animal eats, and increases in size) 
occupies sometimes one stage in the development, sometimes another; sometimes, as for 
instance in the case of Chloéon, now to be described, it continues through more than 
one,—or, in other words, growth is accompanied by development. 
But, in fact, the question is even more complicated than this. It is not only that the 
larvee of insects at their birth offer the most various grades of development, from the grub 
of a Fly to the young of a Grasshopper or a Cricket; we have not to deal only with a 
simple case of gradation, but we have a series of gradations, which would be different 
according to the organ which we took as our test. We have already seen that the larvee 
of Phryganea and those of Diptera and Hymenoptera differ in the development of the 
viscera and of the appendages,—the viscera being in the two latter orders formed before 
a m m 
