MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
537 
[Plate XXXVI. fig. / • «• &•]• Carus has noticed a similar structure in the Grylli , but 
has not described it further than as resembling an eyelid*. He seems to have thought 
it simply a reduplication of the mucous membrane, but has taken no notice what- 
ever of the muscles belonging to it. 
The Muscles concerned in Respiration. 
The muscles concerned in the function of respiration, besides those which properly 
belong to the spiracles, include those of each entire segment of the body. Every act 
of inspiration is of a mixed character, and is partly a voluntary effort of the animal, 
and partly dependent upon those combined laws of the animal economy which, de- 
pending upon each other for their continuance, constitute organic life. These laws 
have j ustly been designated the involuntary functions of the body. Every act of ex- 
piration, in the natural state of the animal, is more of an involuntary than of a volun- 
tary character, and maybe regarded simply as a disposition in the muscles concerned 
to regain their previous condition, which is intermediate between contraction and re- 
laxation, and takes place independently of the will of the animal. 
As every act of respiration thus consists of two distinct efforts, it necessarily re- 
quires the consentaneous action of all the muscles of the parietes of the abdomen and 
trunk in vertebrated, and of all the muscles of a segment of the body in invertebrated 
animals. This is really what takes place in respiration. In Man all the muscles of 
the chest and abdomen are in constant action ; so are all the muscles of the segments 
in insects, whether the animal be awake or sleeping. 
The muscles of a segment of the body in the larva of Cossus ligniperda have been 
minutely described by Lyonet, but as I shall presently have occasion to notice the 
particular nerves which are distributed to them in the Sphinx ligustri, I must be 
permitted to describe those of the ventral surface of a segment in the larva of that 
insect 
Those muscles which form distinct layers or sets, and act together, are generally 
inserted into slightly elevated ridges in the skin, while a single muscle, or the tendon 
of many muscles united together, is attached to a tuberculated elevation. The skin 
is there thicker than in other places, and thus affords a means of attachment. There 
are always three ridges for the insertion of muscles between two abdominal seg- 
ments. The middle one is the largest, and affords both origin and insertion to the 
straight or longitudinal muscles, while the others in like manner afford origin and 
insertion to the oblique ones. 
On removing the fat and viscera from the abdomen of the larva, the first layer 
which presents itself, and forms the interior parietes of the body, consists of many 
longitudinal fibres, like the recti ahdominales of vertebrated animals. These muscles 
extend from the anterior part of the under surface of the second segment to the pos- 
terior part of the eleventh and twelfth ; but it is only at the commencement of the 
* Carus, Comparative Anatomy, by Gore, 1827, vol. ii. p. 162. 
MDCCCXXXVI. 3 Z 
