Dec. 20, 1915 
Biology of Apanteles militaris 
499 
having been drawn through the rudimentary tube into the heart, is 
there passed along by a series of wavelike motions into the head, the 
valves preventing the return of the blood. From here it circulates 
through the body in returning to the caudal vesicle, the walls of which it 
bathes before starting on a new cycle. A careful examination of the 
heart does not show that ostia are present; hence, the blood necessarily 
follows the course described above. 
The silk glands can be distinguished early in this stage and lie on either 
side of the stomach as two straight tubes which meet anteriorly in the 
head and extend to the spinneret. As the end of this stage approaches, 
these glands begin to coil, taking on a wavy appearance. 
Second instar (PI. L, fig. 6 ). —The second instar averages 5^5* 
days, terminating when the larva emerges from its host, for it molts at 
this time. During this stage the average increase in length is from 3.5 
to 6 mm., although when a great many larvae are present in a host their 
size may be reduced nearly one-half. The caudal vesicle normally during 
this stage reaches the length of 1 mm. (Pi. L, fig. 6). 
The head of the larva is made up of 2 segments. The anterior one 
bears a few spines about the oral region and is much smaller than the 
posterior and almost wholly retractile in it. There are no notable charac¬ 
ters or ornamentations on the segments of this larva. The body has 11 
segments and is at first slightly darker than the first instar, but rapidly 
becomes more so as the fat body accumulates. The mouth parts are not 
developed, nor are those of the third instar ready for use, until the larva 
is ready to emerge from its host; hence, it is seen that only the blood and 
the solid matter contained in it are used for food during this stage. In 
older forms there are 7 hyaline areas protruding on each side of the body 
lying between the segments. 
The silk glands grow rapidly, becoming more and more coiled and 
twisted, and are readily seen lying on either side of the alimentary tract, 
nearly filling the body cavity. 
The heart and the circulation of the blood are the same as in the first 
instar. 
The nervous system consists of the supraesophageal and the subesopha- 
geal brains and 11 ganglia with their branches, as in the first instar. In 
the early life of this stage the imaginal discs of the compound eyes are 
noticeable and appear to be in the first thoracic segment. The exhaustive 
studies of Seurat (7) show clearly that although other authors have 
thought that a portion of the prothorax entered into the composition of 
the head of the pupa, it is formed only from the head of the larva and 
that in the larval forms a portion of the head has simply been thrust back 
into the prothorax. Ventrally in the thoracic segments the three pairs 
of imaginal discs of the legs are present, and laterally in the mesothorax 
and metathorax those of the wings can be seen. 
