Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Todd, Robert Bentley
jecting and apparently unwieldy structures 
are rendered exceedingly light, while their 
solid exterior fits them for all the purposes of 
strength required by the insect. The large and 
apparently heavy body of the humble-bee is 
lightened in a similar manner. In this insect 
and others of the same order, the vesicles are 
fewer but very much larger than in Coleoptera. 
The lateral tracheæ in the abdomen form one 
continuous chain of dilatations, which are 
larger in the males of the species (Jig. 436) 
Fig. 436. 
The lateral and inferior series of vesicular respi¬ 
ratory organs in the abdomen of a male individual of 
Bombus terrestris. (Newport, Phil. Trans.') 
than in the females. The longitudinal tra¬ 
cheæ (a), that pass backwards from the 
thoracic region, are connected just as they 
pass through the petiole or thoracico-abdo- 
minal segment into the abdomen, by a very 
short transverse branch (b), which gives off 
two pairs of minute branches into the ab¬ 
domen. The longitudinal tracheæ (c) pur¬ 
suing their course onwards are dilated, soon 
after they enter the large first segment of the 
abdomen, into two enormously expanded 
vesicles (f), above which is placed transversely 
a third and much larger one, which is formed 
from the anastomosing branches of the opposite 
sides of the segment, and is also connected 
with the little branches given off from the 
transverse branch (b). Beneath this large 
vesicle passes the dorsal vessel, and between 
the two lateral ones (_/*) the alimentary canal. 
Besides the branches from the transverse tracheæ 
(6) there are two others from the large tra¬ 
cheæ (c), which pass longitudinally backwards, 
one on each side of the oesophagus. That on 
the left side (e, e) passes as far as the posterior 
part of the proventriculus, and then turning 
forwards distributes its branches to that organ. 
The other on the right (d, d) extends no farther 
than the anterior part of the proventriculus, 
immediately behind the crop or honey-bag, 
upon which it is chiefly distributed. The large 
vesicle (f) is connected with the dilated 
tracheæ in the succeeding segments, and the 
whole form one continuous irregularly-shaped 
vesicular cavity, which, along its under surface 
in each segment, is dilated into a funnel-shaped 
transverse trachea (g), that anastomoses with its 
fellow of the opposite side, passing beneath 
the muscles as in the larva. From the upper 
surface of the longitudinal canals similar fun¬ 
nel-shaped dilatations (i, k) pass over the 
dorsal surface of the abdomen and anastomose 
in like manner with those of the opposite side, 
besides which single undilated ramifications of 
tracheæ (A) pass inwards on each side and are 
distributed over the alimentary canal. At the 
posterior part of the body the vesicular canals 
communicate directly by a large branch (/), 
from which large trunks are given to the colon 
and organs of generation. Thus, then, the 
use of the vesicles is distinctly indicated, even 
in the peculiar distribution of undilated tracheæ 
to the whole of the organs of nutrition. The 
distribution of single ramified tracheæ from 
large vesicles appears to be constant in this 
order ; it was formerly shown by Leon Du- 
four* in Scolia hortorum, and we have always 
found it in the IchneumonicUe and other fami¬ 
lies. Burmeister states that he has been un¬ 
able to ascertain whether this is also the case in 
Diptera, in which order the vesicles are both 
large and numerous. According to Marcel de 
Serresf the Asilidæ have an immense number 
of small elongated vesicles on each side. In 
one species they amount to so many as sixty. 
Burmeister remarks! that, in Lepidoptera, the 
vesicles in the Sphingidee and moths are chiefly 
found in the males, which agrees with our own 
observations in Hymenoptera. In Acherontia 
Atropos he states also that the existence of 
spiral fibre in the vesicles is so distinct as not 
to be doubted. 
This is the structure of the respiratory 
organs in volant insects, but throughout the 
class, whether in volant or creeping insects, 
there is always a complete anastomosis of the 
tracheæ on one side of the body with those on 
the opposite, as has been well exemplified by 
almost all insect anatomists, Swammerdam, 
Lyonet, Marcel de Serres, Dufour, Straus, and 
The development of the vesicles begins to 
take place at about the period when the larva 
ceases to feed, preparatory to changing into the 
pupa state. At the time when the larva of the 
Sphinx enters the earth, and is forming the cell 
in which it is to undergo its transformation, 
the longitudinal tracheæ of the second, third, 
fourth, and fifth segments become a little en¬ 
larged. In the butterfly, Vanessa urticœ, 
which does not enter the earth, but suspends 
* Journal de Physique, Sept. 1830. 
f Mémoires des Muséum, tom. iv. p. 362. 
$ Op. cit. p. 181.


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