THE METAMORPHOSES OF THE NER VO US SYSTEM. 35 
imago, or perfect insect, they fill up the greater part of the 
cavity which encloses them. In every case these cerebral gang- 
lions are more or less united centrally, so as to form a bilobed 
mass. 
The nerves of the eyes (optic nerves), of the antennae, of the 
upper lip, and of the cords which encircle the gullet and unite 
with those of the series of enlargements already noticed, spring 
from the bilobed mass or brain, and also a series of nervous 
fibres, which supply the digestive organs. 
In some insects which have two kinds of eyes, the simple 
ocelli are situated in the middle of the head, immediately above 
the brain — in the bee, for instance. These eyes are furnished 
with a nerve from each side portion of the brain — a pair of 
nerves. They are very short twigs, and are called the first pair. 
The antennae are supplied by the second pair, which originate 
from the under side of the brain, and pass forwards, having 
oftentimes a considerable swelling upon them, into the so-called 
“ feelers.” The size of these nerves depends upon the develop- 
ment of the antennae, and therefore they are much larger in the 
adult than in the early condition of insect life. 
The nerves which supply the side eyes are usually so large 
that they seem to form a part of the brain from which they 
spring ; but there are many insects which, possessing small 
optical organs, have correspondingly puny optic nerves. These 
nerves form the third pair, and like those already mentioned, 
have their size in direct relation with that of the organ they 
supply ; consequently, they only begin to attain a considerable 
growth in the middle life of the insect — in its pupa or nymph 
condition. 
Some larvae which are blind have very delicate optic nerves. 
In others which have several ocelli grouped together on either 
side of the head, and which will become altered into a pair of 
compound eyes when adult age commences, the nervous fibrils 
are numerous. These unite near the brain in early life, and 
form large and closely-connected masses as the development 
of the eyes progresses. The larva of Dytiscus affords a good 
example of the separate condition of the nervous fibres sup- 
plying the mass of simple eyes ; and the examination of the 
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