82 M.H. Rathke on the Respiratory Process in Insects. 
In general the cutis of the abdomen has several transverse 
bands, upon each of which the epidermis is harder and thicker 
than im the space between it and the next band ; and it is only 
exceptionally that in some insects the spaces between the 
bands are either only represented by a constriction or completely 
unrecognizable. But when a thinner and softer skin is inter- 
posed between two bands, the posterior and smaller one is 
generally more or less immersed in the preceding, so that its 
anterior margin is more or less concealed by the posterior margin 
of the latter. Hach band usually consists of two distinct halves, 
an upper and a lower one, united at the sides of the body, like 
the bands themselves, by a thinner and softer part of the cutis. 
In many insects, especially the Hymenoptera, the upper half or 
plate of most of the bands embraces the lower one more or less ; 
but this is not the case in the majority, in which the softer part 
between the upper and lower halves may be recognized from 
without ; this becomes broader and more distinct in proportion as 
the sexual organs are dilated by their products, or the intestinal 
canal is filled with food. 
The muscles by which the hardened parts of the abdominal 
skin are united and moved are so arranged, in most insects, as 
only to approximate these parts; by which they only diminish 
the cavity of the abdomen, and produce an exspiration. Hence, 
in the following memoir, whenever the abdominal muscles are 
spoken of without any special qualification, those which relate 
only to exspiration are intended. The means by which the 
hardened parts of the skin are again separated, and the cavity of 
the abdomen again dilated, to produce inspiration, will be referred 
to hereafter. 
§ 3. In most Coleoptera it is the superior wall of the abdomen 
that moves in respiration, being alternately depressed and ele- 
vated. This movement, however, does not extend in all over 
a relatively equal portion of the abdomen. In those whose 
elytra extend over the whole abdomen, all the belts or segments 
of this division of the body, with the exception of the last, usually 
take part in the movement ; whilst in those, such as Scarabeus 
and Cetonia, whose elytra do not reach so far, the penultimate 
and even the antepenultimate segments take no part in it, which 
is indeed the case with all those segments which are of nearly 
equal thickness throughout and forma simple ring. Movement 
is observed in all those segments in which the epidermis of the 
ventral and lateral walls presents a firm plate, but in which that 
of the dorsal wall forms a thinner and usually smaller plate, 
separated by amembranous interspace at its ends from the above- 
mentioned larger plate, and at its anterior and posterior margins 
from the similar neighbouring plates. The movement is gene- 
