32 M.H.Rathke on the Respiratory Process in Insects. 
plates is united to the next one by a pair of rather broad and 
strong muscular bands (the muscles uniting the upper plates are 
much weaker) ; so that the abdomen can probably be a good deal 
shortened. For the contraction of the abdomen upwards. and 
downwards, several pretty long and almost bacilliform muscles 
pass from the upper to the lower plates in the vicinity of the 
lateral margin. ‘The first two segments have each only one pair 
of such muscles; the segments from the third to the sixth pos- 
sess each two pair, one close behind the other. The soft skin 
can also probably be drawn inwards; for on each side of the ab- 
domen are several short muscular bundles, of which one always 
runs from one end of each lower plate, obliquely from before 
backwards, and a second, partly covering the former, from behind 
forwards to the soft skin, to which they are attached. Two other 
pairs of muscles on each side go from the upper plate to the soft 
skin—one of these, the largest, from the middle of each plate, 
the other from its posterior margin. : 
§ 14. In Truwalis the organization of the wall of the abdomen 
is almost exactly the same as in the larger Acridia. 
§ 15. All the Hymenoptera aculeata, with the exception of 
the Ants, have, according to the author, essentially the same 
organization of the abdomen and respiratory movements. 
Each segment, except the first, consists of two very firm 
plates, generally very broad in proportion to their length, both 
nearly of the same length, and united at the sides of the body 
by a softer skin in such a manner that the upper one projects 
over the ends of the lower one, and therefore the soft skin 
uniting the two plates cannot be seen from without. All these 
segments are also pushed into each other like the tubes of a tele- 
scope; so that the soft skin uniting them is likewise usually 
concealed. In most of these insects the anterior angle of each 
extremity of the lower plates of most of the segments projects 
greatly, forming a point, directed forwards. (The author observed 
in a Bee, the species of which he could not determine at the time 
of making the observation, that between each of these angles and 
the corresponding end of the upper plate there was a small and 
nearly lenticular cushion, consisting of a completely closed, white, 
opake, and rather firm sac, the walls of which were very thick in 
proportion to its cavity.) 
The respiratory movements are effected with great quickness 
and vivacity, are rarely interrupted, and give the insect a restless 
agpect ; they consist in an alternate abbreviation and elongation 
of the abdomen, the individual segments being drawn more 
deeply one into the other and again pushed out. In those which 
have the abdomen nearly straight, such as the Wasps, these 
movements usually take place in a straight direction ; but in 
