68 
POPULAE SCIENCE EETIEW. 
mistake, he lias been at pains to make a work, that was intended merely as a 
popular one, do service of a good kind to both, naturalists and the public 
generally. We believe that it is he who introduced much that relates to 
the nervous system of insects, for we find in this work a great deal of 
matter that is absolutely new to popular treatises. Especially so is the 
account of the development of the nervous system in the larva of Vanessa 
urticce, which is taken from that wondrous worker among insects, our 
English Newport, and which is briefly as follows : — “ Two hours after the 
larva of Vanessa urticce has suspended itself to undergo its transformation, 
and in which state it remains from six, eight, ten, or even twenty-four 
hours — according to the strength of the individual, and other circumstances — 
before it throws off its last larva-skin, a considerable alteration has already 
taken place in the body of the larva. The ganglions in the head are still 
distinct from each other, but are a little in form, although not yet enlarged. 
The sub- oesophageal ganglion is enlarged to nearly twice its original size, 
and the cords which join it to the brain are shortened, and so are those 
that connect the second, third, fourth, and fifth ganglions. The last two 
are separated only by a short interval. The fifth, sixth, and seventh are 
drawn closer together, the ends between them are disposed in a zig-zag 
manner, and the longitudinal direction of the nervous chain is in consequence 
altered. The ganglions, from the seventh to the terminal one, remain as in 
the active larva. A little while before the old skin is thrown off there is 
great excitement throughout the body of the insect. About half-an-hour 
before this occurs there is a considerable enlargement of the brain, the sub- 
oesophageal, and the second, third, fourth, and fifth ganglions. The cords 
that extend between them diverge very much, and those between the fifth, 
sixth, and seventh are disposed in a zigzag direction. Immediately after the 
insect has entered the pupa state all the ganglions are brought closer together, 
in consequence of the ends being disposed more irregularly than at any other 
period, which has been occasioned by the shortening that has taken place in 
every segment, by which the cords are rendered too long to lie in a direct line. 
Seven hours afterwards there is a greater enlargement of the brain, optic 
nerves, and ganglions of the thoracic segments, which begin to approach 
each other. At twelve hours the thoracic ganglions have united, and at 
eighteen the nerves of the wings have increased in size, and the nervous 
chain in the abdomen has become straight again. At thirty-six hours the 
optic nerves have grown nearly as large as the brain, and the gullet is com- 
pletely surrounded by an extension of the ganglion under it, and the brain 
above. The sixth ganglion has disappeared ; and at the end of forty-eight 
hours the seventh is no longer seen, but the thoracic centres increase in 
size gradually. At fifty-eight hours the middle part of the chest has 
greatly increased in size, and the great nervous centres and nerve twigs, 
which will supply the wings eventually with energy, occupy it. The optic 
and antennal nerves have nearly attained their full development, and the 
arrangement of the whole nervous system is now nearly as it exists in the 
perfect insect. The whole of these important changes are thus seen to take 
place within the first three days after the insect has undergone its meta- 
morphoses, and they precede those of the digestive system.” We have given 
this rather long quotation for various reasons : in the first place, it illustrates 
