INTERNAL ANATOMY OF INSECTS. 7 
while the medullary part was white? ; Cuvier relates that 
the brain and the third ganglion in Hypogymna dispar, 
with us a scarce moth, differed in colour from all the 
rest, being quite white, while the others were more or 
less tinted, and examined under a lens appeared varie- 
gated by reddish sinuous markings, resembling blood- 
vessels as they are seen in injected glands®. 
II. Tunzcs.—The coats that inclose the various branches 
of the nervous system in insects seem analogous to those 
of vertebrate animals. The first thing that strikes the 
eye, when these parts in a recent subject are submitted 
to a microscope, is a tissue of very delicate vessels, which 
ramify beyond the reach of the assisted sight; these are 
merely air-vessels or bronchi derived originally from the 
trachee of the animal: but besides these is an exterior 
and an interior tunic; the first corresponding with the 
dura mater of anatomists; and the other, which is the 
most delicate and incloses the cortical and medullary 
parts, with the pia mater °. 
III. Parts.—The nervous system of insects consists 
of the brain ; the spinal marrow and its ganglions ; and 
the nerves. 
i. Brain‘, Linné denied the existence of a brazn in 
insects, and most modern physiologists seem to be of the 
same opinion. A part however, analogous to this impor- 
tant organ—at least in its situation, and in its emission of 
nerves to the principal organs of the senses, in which re- 
spect it certainly differs very materially from the upper 
2 Malpigh. de Bombyc. 20. Swamm. Bibl. Nat. 1. 224. a. 
b Anat. Comp. ii. 348. 
¢ Lyonnet Anat. 100. ¢. iv. f. 6. Sandwith Introd. 59—. 
4 Prare XXI. Fic. 1. 7. 8. a. 
