317 
1915-16.] Structure and Life-History of Bracon sp. 
and below these two regions representing the maxillae and labrum. Eyes 
are wanting. 
The larvae is active, and crawls rapidly about over its host. It is not in 
any way attached to it except when feeding, when it buries its head in the 
folds of the skin of the Hylobius larva. 
At this stage there are no signs of tracheae or of spiracles, but the 
alimentary sac appears as a greyish mass shining through the skin. 
The first instar lasts for one or two days. (Plate I, fig. 4.) 
The Second-Stage Larva. 
At the first moult the larva undergoes a marked change : the tiny hairs 
or bristles, that were so striking a feature of it, disappear. The head is 
much smaller proportionately, and the body no longer tapers posteriorly. 
The larva is now broadest at its middle, tapering anteriorly and posteriorly. 
Its length is 1*5 mm. A marked feature of the larva is a number of 
whitish spots shining through the skin. Newport* in his paper on 
Paniscus comments on a similar phenomenon. 
The second instar lasts one or two days. 
The Third-Stage Larva. 
This differs in no way from the second stage except that it is larger, 
32 mm. long. For some time I failed to recognise this third stage, until 
I found in three broods the cast skins of this second change. 
The third instar lasts a day, or a day and a half. (Plate I, fig. 5.) 
The Fourth-Stage Larva. 
At this period the larva measures 5 mm. in length. It is markedly 
different from the preceding stage. The head is now sunk in the first 
segment of the body and almost hidden by it. The antennae are much less 
prominent. The tracheal system is clearly seen, and the spiracles are 
distinct. There are nine pairs of spiracles, viz. a pair on the first segment 
and a pair on the fourth and on each of the seven following segments. 
The whole of the integument is covered with very short reddish hairs. 
Hitherto the segmentation had been extremely simple, consisting of the 
head and thirteen consecutive rings. These body rings now show on their 
dorsal surfaces an additional fold corresponding to the prescutal fold in 
certain Coleopterous larvae. The white spots have now disappeared. In 
general appearance the larva is now a curved maggot, tapering towards 
each end, the head end being slightly broader than the tail. 
The mouth parts of the fourth-stage larva are very similar to those 
* Newport, Trans. Linn. Soc., 1862, xxi, p. 63. 
