168 
J. BRONTE GATENBY. 
seems to be the rule in many Hymenopterous larvae. In the 
oldest larvae I have found there is no oesophageal valve 
formed, nor is there any differentiation in the proctodaeal end 
of the gut. 
As the larva grows it swallows all the host’s yolk in the 
egg, and no defecation takes place until every yolk disci et 
has been swallowed ; by this time the animal is enormously 
stretched, and the body-wall and gut-wall are so thin as to be 
overlooked unless care is taken. PI. 12, fig. 38, is drawn 
when the swallowing is well advanced, PI. 12, fig. 33, when 
the first food has reached the mesenteron. When the larva 
has finished swallowing the yolk, it occupies almost the whole 
extent of the egg. 
The Head Region of the Larva of Trichogramma. 
In PI. 12, fig. 30, I have drawn the horizontal section of 
the head region. The mouth {MTU.) is a simple opening; 
but pointing forwards and outwards are two extraordinary 
horn-like processes {PRC.). These are seen to protrude 
from a pair of lateral thickenings — one on each side of the 
head. These thickenings arise quite early, and are closely 
associated with the inner side of the epidermis. In PI. 12, 
fig. 29, {TH.) 1 have drawn a transverse section of a younger 
head to show the thickenings before the horn is secreted from 
them. Beyond this curious organ I have been unable to 
discover any other mouth parts whatsoever. 
The Late Larva. 
In the stage when the larva has swallowed all the yolk 
several facts may be noticed. 
The first is absence of tracheae ; the second, absence of any 
external sign of segmentation ; and the third, the absence of 
completely differentiated muscles or heart. 
The larva is merely an ovoid sac, provided in front with 
two horn-like processes, and with an opening at either end, 
for taking in food and casting out waste matter ; internally 
there is a gut divided as usual into three regions ; and finally 
