532 
MR. NEWPORT ON THE RESPIRATION OF INSECTS. 
substance of fibres, as I have distinctly seen them in the vesicles of the male Humble- 
bee, Bombus terrestris, Steph. Besides this, I have also observed them terminating 
in an abrupt and remarkable manner in the dilatation of the large tracheae in the 
same insect ; and I have also seen them in some of the larger tracheae themselves, 
as was observed and figured by Swammerdam in Oryctes nasicornis, Steph. The 
existence of these punctured spots so universally in perfect volant insects, leads us to 
inquire into their probable use. After many careful examinations I am disposed to 
believe that these spots are only partial perforations of the vesicular structures, — that 
they do not pass through the internal or mucous lining, — -and perhaps are little cells 
or receptacles in the coats of the vesicles, in which the circulatory fluid can be most 
freely submitted to the action of the air in the vesicles through the delicate mucous 
lining, as in the minute terminal air-cells in the respiratory organs of vertebrated 
animals. 
When the tracheal vessels have become developed into pulmonary sacs, those of 
each segment may be considered as analogous to, and as only a repetition of, the 
tracheal structures in Vertebrata. A very large proportion of the ramifications from 
each centre or spiracle in the larva of the Sphinx and other Lepidoptera is distributed 
over the alimentary canal. Those which are given to the oesophagus and stomach 
extend from the second to the tenth segment, while those which go to the duodenum 
are from the eleventh, and those to the colon and caecum from the twelfth and thir- 
teenth. The minute branches of these vessels pass between the fibres of the muscular 
coat of the alimentary canal, and are distributed upon the mucous coat, between it 
and a structure which I believe has not hitherto been described, the adipose coat , 
which lies between the mucous and muscular coats, and into which the ultimate 
ramifications of the tracheae are extended. This layer is very distinct in the ali- 
mentary canal of Cerura vinula , Steph., particularly in the colon and caecum 
[Plate XXXVI. fig. 3. a. bd\. All the secretory and generative organs are furnished 
with minute anastomosing branches in abundance, even the dorsal vessel itself, and 
the ovarial tubes. They are distributed through the limbs, even to the extremities 
of the tarsi in the perfect insect, and through the antennae and eyes. 
The development of the air-vessels into sacs or bags in volant insects begins to take 
place a little before the insect changes into the pupa state. In all larvae which undergo 
a complete metamorphosis, when passing into the pupa state, the respiratory organs are 
distinctly tracheal, without any dilatations ; and this is more strictly the casein those 
insects which afterwards have the largest vesicles, as in the Scarabcei. Lucani, Lepido- 
ptera, and Hymenoptera. In lepidopterous insects the tracheae do not appear to undergo 
any marked change until about the time when the insect has ceased feeding. Those 
which are the first dilated in the Sphinx are from the second and fifth spiracles. 
These, with the anterior portions of the longitudinal tracheae, become a little dilated 
soon after the insect has entered the earth, and is forming the cell in which it is to un- 
dergo its transformation. In the Butterfly [Vanessa ?«^zcce,STEPH.),which does not enter 
