INSKCTA. 
329 
They all have two anteinice and a distinct head. The nervous sys- 
tem of most Insects — the Hexapoda — is generally composed of a 
brain formed of two opposing ganglions, united at base, giving off 
eight pairs of nerves and two single ones, and of twelve ganglions* *, 
all inferior. The two first are situated near the junction of the 
head with the thorax, and are longitudinally contiguous ; tlie anterior 
sends nerves to the lower lip and adjacent parts ; the second, third 
and fourth belong to each of the three first segments, or those which 
form the thorax in the Hexapoda; the remaining ganglions belong 
to the abdomen, so that the last or the twelfth coiTesponds to its 
seventh ring, and is immediately folloAved by those which compose 
the organs of generation ; each of these ganglions transmits nerves 
to the parts of its respective segments. The two last, wliich are 
closely approximated, also send some to the terminal annuli of the 
body. The frontal region exhibits three particular ganglions called 
frontal by Lyonet, from the first of which arises posteriorly a great 
nerve with enlargements, the longest of all, that he denominates the 
recurrent. The first ordinary or sub-oesophagean ganglion, gives 
off, according to him, fuirr pairs of nerves, and each of the following 
ones, two; so that by counting the eight pairs of the brain, and the 
ten spinal bridles, which may also be considei’ed as so many pairs of 
nerves, we shall have in all forty-five pairs, exclusive of the two 
solitary nerves above-mentioned, or from twelve to fourteen more 
than are found in the human subject. The two nervous cords which 
form the ganglions by their union, are tubular and composed of two 
tunicks, in the exterior of which we observe tracheae ; a medullary 
substance fills the central canal. Tlie admirable work of M. Herold 
on the anatomy of the larva of the great Papilio brassica’, L., 
studied throughout its various degrees of developement, and to the 
period of its transformation into a chrysalis, shows us that the ner- 
vous system and that of the digestive organs experience remarkable 
changes ; that in the beginning, the nervous cords are longer and 
further apart, an observation which strengthens the opinion of one 
of the greatest zootomists of the age. Doctor Serres, on the origin 
and developement of the nervous system. In our general remarks 
on points common to the three classes of articulated animals provided 
with articulated feet, we mentioned the various opinions of physi- 
tra, there is none in the second segment or mesothorax ; but in the following one 
or the metathorax, there are two pairs, one anterior, which being situated near 
the articulation of this segment \Yith the preceding, may be considered as belonging 
to the latter, and the other smiiller, and placed close to that of the first abdominal 
segment. 
* Several of the Lamellicornes in a perfect state form exceptions. 
