346 Mr. Ngwronr on the Natural History 
imperfect respiratory organs, of the nature of branchiz. A branchial form of 
respiratory organs we know exists in the aquatic larvae of insects which, in 
their perfect state, respire atmospheric air, and it is not improbable that a like 
condition of the respiratory organs exists in the early states of this parasite. 
The larva of Ichneumon atropos, however, in which I have found that there 
certainly is no outlet to the alimentary canal, and which, as before stated, 
subsists on the adipose tissue and fluids of the caterpillar, has true, but ex- 
tremely minute spiracles and air-vessels, and although completely inclosed in 
the body of the caterpillar, seems to respire the air directly, perhaps from the 
injured air-vessels of its victim. 
DEVELOPMENT or THE LARVA OF STYLOPS. 
When the young Stylops has penetrated the body of the bee-larva, shut up 
in its cell in the earth in the spring, it grows as rapidly as the larva itself is 
nourished. It certainly changes its skin once, and perhaps oftener, like other 
insects. Its need for organs of locomotion, and for the perception of surround- 
ing objects, is then reduced toa minimum. Accordingly, as I shall presently 
show takes place also in Meloé, inclosed in the cell of Anthophora, the legs 
with which the young Stylops was provided when it issued from the body of 
its parent become atrophied, and their further development is so completely 
arrested in every part, owing, perhaps, to the excess of growth which is taking 
place in its other structures, that they entirely disappear, being first reduced 
to their merest possible rudiments, pedal papillae, which are more and more 
reduced in size as the growth of the body proceeds. On the other hand the 
body of the Stylops becomes so enlarged by the nourishment ingorged from 
the substance of the body of the bee-larva, that its entire form and propor- 
tions are completely changed. . 
During the period of its growth, the parasite, as found by Dr. Peck * in 
Xenos, lies with its head in the direction of that of the insect preyed upon,— 
that probably in which it entered the body. But when it has arrived at its 
full growth, and is about to change to a nymph, its position in the body is 
reversed, and adapted to its future exit backwards between the rings of the 
abdomen of the hymenopterous insect. Its change to a nymph takes place in 
* Trans. Linn. Soc. vol. xi. 
