94 M.I1. Rathke on the Respiratory Process in Insects. 
directed somewhat obliquely backwards from their points of 
origin. 
§ 16. In the Hymenoptera with an ovipositor (Terebraniia) 
the author’s observations were made chiefly on Ophion luteus, 
Ichneumon persuasorius, and Sirex gigas. In these the upper 
plates of the abdominal segments are considerably larger than 
the lower ones, and form both the dorsal and lateral walls of the 
abdomen ; the lower plates occupy only the ventral wall. The 
former also project a little beyond the latter, with perfectly free 
extremities. 
In the respiratory movements the lower plates are usually 
somewhat elevated and again depressed; more rarely, and only 
when the respiration is very forcibly effected, the ends of the 
upper plates are also set in motion inwards and outwards. 
The trachez are shrub-like ; and no air-sacs ever occur. 
Details. 
In Ichneumon persuasorius the lower plate of each of the first 
eight segments of the abdomen is rather broad; the first is 
simple, the rest partly hard and partly soft. The harder and 
thicker parts form three longitudinal bands,: of which the 
broadest occupies the middle of the plate, the others lying close 
to its lateral margins. Between these and the middle band are 
two softer bands, which in the specimen examined were a little 
bent in towards the ventral cavity; so that each plate, viewed 
from beneath, showed two moderately broad and deep furrows 
running in the direction of the length of the abdomen. During 
exspiration the entire plate moved upward, and during inspira- 
tion downward ; and in the latter act the above-mentioned fur- 
rows were not unfrequently effaced, so that the plate became 
quite flat and a little widened. On the abdomen being opened 
it appeared that on the convex side of each of the furrows there 
was a longitudinal muscle running from the anterior margin of 
each plate to the same margin of the following one: from its 
position and attachment, its contraction must flatten the furrow- 
like part. A second, shorter and flatter muscle passed from each 
anterior angle of the lower plates, outwards, upwards, and back- 
wards, to the upper plate of the same segment; these serve for 
exspiration. (Superior longitudinal muscles were also present.) 
In the female of Sirex gigas the two hindermost segments of 
the abdomen have no inferior plates ; in the other six segments 
the lower plates are present and very broad. From each anterior 
angle of these plates a moderately strong exspiratory muscle 
passes upwards, outwards and backwards to the upper plate of 
the same segment. Another much thicker and Jonger mus- 
cle, also serving for exspiration, passes from each posterior angle 
