472 MAUD D. HAVILAND 
from the host’s tissues. It is possible that the structure of the 
anus and proctodaeum is correlated with this, and that some- 
thing analogous to rectal respiration exists in this form. The 
hind-gut has a large lumen enclosed by modified hypoderm 
cells. In the later stages the proctodaeum is proportionately 
smaller, and, when the chitin is cast off, respiration is pre- 
sumably carried on through the cuticle, as in such forms as 
Aphidius, though mention should be made of the tongue- 
shaped process of large deeply-staining cells, which, like 
a typhlosole, projects into the lumen of the proctodaeum as 
development proceeds, and, if the view suggested here is correct, 
would increase the respiratory area. 
A peculiar modification of the hind-gut occurs in the larvae 
of certain Braconids, suchas Apanteles and Microgaster. 
The body terminates in a hollow bladder or vesicle of hyper- 
trophied cells ; and Gatenby (8), who has recently re-deseribed 
this structure, makes the interesting suggestion that this is 
morphologically the proctodaeum, which has become everted 
for respiration. The enlarged, though uneverted, hind-gut 
of Charips may be intermediate between the highly-special- 
ized structure found in these Microgasterinae and the 
unmodified proctodaeum of most hymenopterous larvae. 
It is noteworthy that in these Cynipidae great development 
of chitin is associated with unusually short Malpighian tubules. 
If the chitin persisted throughout larval life we might be 
tempted to regard it as a means of disposing of such nitrogenous 
waste material as could not be dealt with by the tubules. 
But as the chitinized plates are lost early, while the tubules do 
not increase in size in the later stages, it is improbable that the 
two characters are correlated. 
REACTION OF THE Host. 
Aphidius reacts very differently to Charips and to 
Lygocerus. In parasitization by the latter, as described 
elsewhere (10), the host dies, and speedily deliquesces into 
a mass. Nothing of this kind happens where the Braconid 
contains a Charips larva. The Aphidius demolishes 
