274 CLASS VIII. 
tortuous in the pupa, and shorter in the perfect Insect ; the nervous 
ganglia become less numerous, from some of them first approxi- 
mating to each other and afterwards coalescing, whilst others 
entirely disappear; the first ganglion especially, which is situated 
in the head, increases in amplitude. The sexual organs, of which 
the germs already existed in the larvae, become developed as well 
in respect of complex structure as of size. In the pupa new organs 
also come to view, of which before there was no trace, such as the 
wings, which are seen folded and rolled together imternally at the 
thorax. The dorsal vessel undergoes less change than most of the 
other organs. 
There is in larvae, moreover, a peculiar fatty mass present, of 
which we have already spoken above; the secretion of this fat 
constantly increases, the nearer the larva approaches the condition 
of pupa; in this condition the fat is consumed again, and in that 
of the perfect Insect, when it also takes food, fat is no longer 
secreted. 
The fatty secretion is thus obviously necessary to supply nutri- 
ment to the pupa, and to afford the material for the development 
of the organs of the perfect Insect. Yet the pupe of Insects 
which undergo a complete metamorphosis, take, as stated above, 
no food, and are in connexion with the external world through 
respiration alone}. The condition of pupa therefore may be com- 
pared with that of hybernating animals, which are very fat in the 
autumn, during their sleep take nothing, and in the spring come 
out of their retreats in a very emaciated condition. The larve of 
Insects eat more than is necessary for their own growth; they are 
therefore usually inactive; deficient motion and superfluous food 
favour, as is known, the secretion of fat?. The reason why in 
perfect Insects no more fat is secreted, is found as well in the 
development of the sexual functions as in the greater activity of life 
and rapidity of motion, which are peculiar to them. 
1 On this account they lose in weight. This loss is, however, at first very small, 
and only becomes remarkable on the approach of the last change. See NEWPoRT in 
Topp’s Cyclop. 11. pp. 879, 880. 
2 That this fat is not necessary for the life of the larva, is shewn by the examples 
of caterpillars in which ichneumons have deposited their eggs; the larva from these 
consume the fat of the former, which die from the robbery of their stock of food only 
at the time they should change into pupz, or have changed. 
‘a. 
