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 wavehke 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 5r2- 

 days, tenninating when the lar^-a 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 i 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 lar\'a. The body has 1 1 

 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 ahmentary 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 1 1 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. 



