M. H. Rathke on the Respiratory Process in Insects. 101 
remain quite quiet: from this we may conclude that the will may 
exert some influence on the respiration. 
- §23. Certain phenomena lead to the belief that in many in- 
sects various viscera have a subordinate action upon the respira- 
tion of insects, or at least upon the distribution of air in them. 
1. The pulsation of the dorsal vessel sets a number of tracheze 
in motion, pushing them forwards and backwards, extending 
them in length, and then permitting them to contract or contort 
themselves again. : 
2. In those insects which possess a sucking-bladder connected 
with the anterior part of the alimentary canal, this must produce 
similar, but sometimes, by lateral pressure, still greater effects 
upon the tracheze and air-sacs in its vicinity: in many such in- 
sects, especially Diptera, this bladder, which is sometimes of 
great size, may be seen, even through the skin, slowly but inces- 
santly contracting and expanding alternately to a very great 
extent. 
3. This applies also to the intestine and, although in a far 
less degree, to the malpighian vessels, which, as may be ascer- 
tained not only from opened insects, but also from many unin- 
jured ones (such as some species of Syrphus), are constantly 
performing peristaltic movements. The strongest peristaltic 
movements, which indeed were perceptible through the walls of 
the abdomen, were observed by the author in Ophion luteus. In 
the first segment of the abdomen, in which the mtestine was 
_ quite straight, they went on unceasingly, in such a manner 
that the portion of intestine contained in it always remained 
straight ; in the remainder of the abdomen, in which the intestine 
is much contorted, they took place only at intervals, but each 
time with great rapidity and violence, the intestine undulating 
to and fro to a remarkable extent. 
_ By the dragging of these viscera upon the neighbouring and 
attached trachez, and also by the pressure which some of them 
exert during their extension upon air-sacs in their vicinity, it 
cannot be but that the air contained in these parts will be set in 
motion. Partial movements of the air in the interior of the in- 
sect must also be produced during the action of the muscles of 
the limbs, as these muscles are penetrated and surrounded by 
many air-vessels. 
II. Imprrrect Insects. 
A. Of those which only undergo a partial metamorphosis. 
§ 24. The structure of the abdomen in the young of Blatta, 
Gryllus and Acridium is similar to that occurring in the perfect 
insects ; so that it is probable that the respiratory process is the 
same in both. 
