392 
latter vessel and pass up these three channels, thus taking a 
second course through the vessels of the wing. The same 
occurs with part of the blood returning by the veins a, a, a. 
This passes by a small branch into the artery a, and so on 
back into the wing, whilst the remainder flows on into the body. 
We can hardly look upon this system of blood-vessels in the 
wing of Blatta as ensheathing the trachez.! These latter are 
very small in comparison with the former, and, moreover, do 
not send any branches into the transverse connecting vessels 
at all. The principal blood-vessels rather have small trachez 
running inside them. In many coleoptera the trachee are 
absent from these blood-vessels. In Melolontha vulgaris there 
are fine tracheal branches at the commencement of the prin- 
cipal vessels only. In most Lepidoptera they are very large, 
the expansion of the wing after emergence from the pupa 
being probably effected by a combined increase of pressure of 
air in these large trachez, and of blood in the vessels in which 
they lie. Of course the extensive circulation in a thin and 
generally moist membrane, such as is the wing of Blatta, 
must cause this latter organ to exercise to a great extent the 
functions of a lung; hence, perhaps, the smallness of the 
tracheze. It is possible also that the absence of these aerating 
organs is compensated in the female Blatta wy the very much 
larger size of the salivary glands. 
Ina paper published in the last number of the ‘ Cambridge 
Journal of Anatomy and Physiology,’ Mr. Ainslie Hollis 
has come to the conclusion that the so-called salivary glands 
of Blatta perhaps act directly as aerating organs; but this 
author seems not to have met with the monograph of J. 
Basch? on the digestive and renal systems of this insect, where 
it is shown that these glands are capable, not only of con- 
verting starch into sugar, but also of digesting albumen. 
Moreover, on opening living specimens of Blatta I have more 
than once found the salivary receptacle, which Mr. Hollis 
has found always full of air, filled with a transparent fluid. 
It is possible that he may always have killed his specimens 
first, and that they may have ejected the contents of the re- 
ceptacle in dying. If, therefore, the larger glands of the 
female compensate the wings of the male, I consider that they 
do so as excretory organs rather than as direct aerators. 
Fig. 3 represents. one of the transverse colourless vessels 
which connect the main trunks. It is drawn from a wing 
hardened in perosmic acid under a Hartnack’s 7. On either 
' Carpenter’s ‘Comparative Physiology,’ 238. 
* “S. Basch Sitzungsberichte, Kaiser Akad. Wiss. Wien,’ vol. 33, 1858, 
p. 234, Matt. Nat. Classe. 
