M.H. Rathke on the Respiratory Process in Insects. 95 
of the lower plates upwards, outwards and forwards to the ante- 
rior margin of the upper plate, covering the broader upper part 
of the above-mentioned muscle. There are likewise upper and 
lower longitudinal muscles for the abbreviation of the abdomen. 
The lower ones are even doubled—two on each side of the lower 
plates. They are rather thick, but narrow. The upper muscles, 
on the contrary, are very broad, but thin and delicate. Notwith- 
standing these numerous muscles, however, the abdomen is not 
shortened and elongated for the purpose of respiration, as in 
Bees and Wasps. 
$17. The author then discusses the question whether these 
movements of the abdomen, supposed to be connected with re- 
spiration, may not subserve some other fnnction. 
1. The pulsation of the dorsal vessel cannot be essentially 
affected by these movements, as when they cease for a longer or 
shorter time the activity of the dorsal vessel does not stop. 
This applies also to the action of the digestive organs, for 
this likewise goes on, and movements (especially peristaltic) of 
the intestine and malpighian vessels take place even when the 
movements of the abdomen cease for some time. There can 
also be no particular relation between them and the function of 
the generative organs, as they occur both when the sexual organs 
are far from maturity and when their activity appears to be 
purely plastic. There are no other organs in the abdomen of 
most insects, except the respiratory organs, with which these 
movements can be connected. 
2. As the latter organs are surrounded by structures far less 
compressible in their nature, it is clear that as the walls of the 
abdomen contract, the air contained in the respiratory organs 
must be set in motion and partly expelled through the stigmata. 
3. The movements of the walls of the abdomen, in those insects 
in which they occur, take place, like the respiratory movements 
of higher animals, more rapidly when the insect makes, or en- 
deayours to make, greater muscular exertions ; hence we may 
conclude by analogy that there is a close relation between the 
movements in insects and those in vertebrate animals. 
4. In Cetonia aurata and Scarabeus stercorarius the author 
convinced himself by observation that these movements truly 
act upon the respiratory organs. On cutting off first the wings 
and wing-cases and then the upper wall of the thorax from these 
Beetles, he saw that every time the dorsal wall of the abdomen 
was depressed the air-sacs contained in the thorax became 
tensely dilated, and when the dorsal wall again rose these air- 
sacs became a little smaller. 
5. In Acridium stridulum he remarked that, whenever the abdo- 
men contracted, the two pad-like and closely appressed lips of 
