84 M.H.Rathke on the Respiratory Process in Insects. 
proportion to the whole body. The dilatations and contractions 
of the abdomen do not follow each other with equal rapidity in dif- 
ferent Beetles ; they appear generally to be rapid in proportion to 
the size of the air-vessels ; in the Beetles examined by the author, 
they succeed each other most rapidly in Cetonia and Scarabeus. 
But here we have to consider whether the animal is quite quiet 
or in motion or troubled, and also whether it has lately taken a 
sufficiency of food or whether it is hungry; for when it has fed 
well or moves, the movements of the abdomen follow one another 
far more rapidly than when it is quiet or fasting. 
Note I1.—The above observations were made on species of the 
genera Cetonia, Scarabeus, Cerambyx, Hister, Dytiscus, Carabus, 
Chrysomela, Tenebrio, Bruchus and Attelabus. It is remarkable 
that im Staphylinus, in which, notwithstanding its differmg so 
much in many respects from other Beetles, the structure of the 
abdominal segments and of their muscles is the same, no distinct 
movement of the upper pieces of the abdominal segments could 
be perceived. On the other hand, the upper part of the third 
thoracic segment was seen to rise and fall alternately, and often 
very considerably. The author could not ascertain whether for 
this movement there are peculiar muscles not occurring in other 
Beetles. He observed, however, that in Staphylinus the widest 
and most important air-vessels occur in the posterior half of the 
thorax. The above-described movements of the abdomen were 
not observed in Coccinella, in which, contrary to the general rule, 
the upper plates of the abdomen are larger than the lower ones. 
In the Carabide also (at least, in C. granulatus) the upper half 
of the last thoracic segment is moveable, and rises and falls a little 
during respiration, although less than the upper halves of the 
abdominal segments. 
Note I1.—In Tenebrio molitor the upper pieces of the abdo- 
minal segments are so transparent, that the intestines, and espe- 
cially a quantity of tracheze which run quite close beneath those 
pieces, may be distinctly seen through them. Many of these 
trachez, especially those which run from below upwards, may be 
seen in constant movement ; they are observed sometimes to be 
alternately stretched out and again curved, and sometimes to be 
moved forwards and backwards. This movement is not proper 
to them, but is communicated by the dorsal vessel to which they © 
are attached. 
Note I1I.—In the vivisection of a Scarabeus stercorarius, the 
author, having removed the dorsal wall of the abdomen and drawn 
forth the intestinal canal a little, by which many small trachez 
‘were torn, was astonished to see several of these trachez move 
very briskly, like worms, in the water in which the Beetle was 
being dissected. For some minutes he supposed that the move- 
