OF THE TRACHEA IN INSECTS. 
25 
Bornbus, where tufts are present in most of the organs, the tubules 
particularly 
numerous on the ovary. On the other hand, this rule is not without numerous excep 
tions-— as, for instance, Ophion, (PI. III. fi 
(PI. III. fig 
- 
Acheta (PI. III. fig. 12), Aphroph 
In every insect which I ha^ 
d it would perhaps not be sale to generalize on the subject 
examined, the ganglia Avere well supplied with trachea? 
and the type was very uniform, showing, I think, that the minute structu 
organs is very similar, not only in different parts 
different insects. 
As regards the commissures, the case is 
•e of these 
of the nervous column, but also in 
quite the reverse : not only does the distribu- 
tion of the tracheae differ much in different groups, but in some, as, for instance, in the 
Neuroptera and Lepidoptera, they are, at least in the perfect insects, almost entirely absent. 
This difference probably arises from the difference in the respective properties and func- 
tions of the j?am?lia and commissures. It is an interesting fact, that while in butterflies 
ally found the commissures free from tracheae, in the larvae they 
- 
o 
and moths I ha\ 
are richly supplied. Is this to be accounted for by supposing that the relative funct 
and structures of the different parts belonging to the nervous system are not so com- 
pletely differentiated in the larva as they afterwards become in the perfect insect ? 
The presence of tracheae on the commissures is not, however, always a sign of low 
development, since the} 
Both the larv 
present in many Coleopt 
and perfect insect of Acheta have tracheae on the thoracic, but hard! 
any on the abdominal commi 
The presence of a few tracheae cannot, however, be 
of any great functional importance, since in insects with double commissures I have more 
than once seen instances in which one only 
provided 
Dr. William 
paper on the respiration of insects, enunciates very confidently 
the following propositions, which he considers to be true without 
which he has since reiterated 
any 
pt 
and 
1st. That 
the larg 
tracheae never anastomose 
that 
a 
plexiform union of the branches ever anywher 
2ndly. " That the ■ spiralled ' or larger 
in the spiral tracheae no 
sr tracheae are mere conduits, like arter 
and have nothing to do with, take no part in, the ultimate act of respiration. 
or 
3rdly 
That the peripheric or extreme distribution of the tracheal system is conform 
able in plan to that of a blood-vascular system ; that is, the capillary or membr 
tracheae are 
they serve to 
alway 
placed intermediately between larger trunks, the branches of which 
standing to the larger trunks in the same relation as the capil- 
gle instance to end in caecal 
laries of a blood-vascular system do to arteries and veins." 
4thly. " That the tracheae can be discovered in no sii 
terminations — always in mutual inosculations." 
I might have passed over the first assertion as a mere momentary slip of the memoir 
if it were not repeated more than once in 1854, and again reaffirmed in 1856. Several of 
the 
figures g 
by Straus-Durckheini, Leon Dufour, and other writers, show inos 
culations of the tracheae : and there 
hardly 
a 
gle insect in which they do not 
* Annals and Mag. of Nat. Hist. 1854, vol. xiii. p. 194 
fib. 1856, vol.xvii. p. 347 
VOL. XXIII. 
E 
