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MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
urgent than in the larva state. Hence it is evident that much caution is necessary 
in drawing conclusions from our observations on the function of respiration in insects 
in their different states, and that where quantity of air is concerned the relative 
volume of the organs of respiration must not be forgotten. 
Parts concerned in Respiration. 
The parts more immediately concerned in respiration are the tracheae and spiracles, 
the first of which undergo very great changes during the transformations of the in- 
sect. The next are the muscles and the nerves distributed to them. 
1. The Tracheae. 
The tracheal vessels in the larva of Sphinx ligustri, L., consist, as described by 
Lyonet and others in the Cossus ligniperda, of a series of tubes conveying air like the 
bronchial tubes and tracheae of other animals ; but instead of being composed of only 
one set communicating with the mouth, as in vertebrated animals, they are multiplied 
in number, and are arranged along each side of the body of the insect near the middle 
line, between the dorsal and ventral layers of longitudinal muscles. There are nine 
sets of tracheal tubes on each side, corresponding to the nine outlets or spiracles. 
The first is situated in the second segment, behind the head, and the remaining eight 
are in the fifth and succeeding segments to the last or anal one. The different sets 
are connected together by two longitudinal tracheae, one on each side of the body, 
and communicate by very short tubes from these tracheae with the spiracles. 
The structure of the tracheal tubes has been described by Swammerdam, Sprengel, 
and others. The tracheae are formed, as described by Sprengel, of two membranes, 
an external serous, and an internal mucous, inclosing between them a spirally con- 
voluted elastic fibre [Plate XXXVI. fig. 1 . a.], which gives them the appearance of 
the tracheae of other animals. The external or serous membrane \_b~\ is very loosely 
attached around the middle or spiral structure. The whole mucous or internal lining 
is continuous with the cuticle or external covering of the body, and is thrown off and 
renewed whenever the insect changes its skin, as noticed by Swammerdam, DeGeer, 
Lyonet, and Bonnet ; although Sprengel seems to consider this as not a true 
membrane, but as only forming a means of connexion between the coils of the middle 
or spiral fibre. I have seen this lining membrane of the tracheae thrown off with the 
skin of the larva at every period of its change in almost every order of insects, but 
more particularly in the genera Apis, Papilio, and Scarabceus, and am satisfied 
that it is a distinct structure, and is not merely that portion of the membrane which 
lines the entrance of the tubes which is thus thrown off, but the complete lining mem- 
brane of the ramified tracheae. 
Each set of vessels consists of from eight to ten or twelve tubes, which originate 
in a bundle from the longitudinal tracheae, and distribute their branches over the 
stomach and other viscera, sending minute anastomosing ramifications to every part 
