1919.] 



23 



which position the host caterpillar adheres to a wall or tree, the majority 

 of larvae attack the sides of the host. This does not seem to be a 

 general rule for other Braconids. In addition, there seems to be some 

 evidence that the larvae have a geotropic sense ; if a parasitized cater- 

 pillar is lying at the bottom of a square box, with its body parallel to 

 the side of the box, and one side facing upwards and the other touching 



Test-fig. 1.— Caterpillar of Pievis brassicae at a time when most of the Apanteles 

 glomeratiis larvae have made their exit from its haemocoel. 



,, 2. — Head region of same showing mode of exit of parasites (P) : t;=leg ; 

 f = thread of silk : to = outer layer of cocoon. 



„ 3 and 4. — Early stages in spinning of cocoon after emergence of larva 

 from body of host (b) : /i = head of larva ; it" — web. 



the floor of the box, almost all the larvae emerge on the uj^ward side. 

 A few may pass outwards on the underside, but not many ; others pass 

 outwards on the true dorsum of the caterpillar, but the majority prefer 

 the upper lateral side. This is the case shown in text-fig. 1. 



In text-fig. 2 the head end of a pai'asitized caterpillar is drawn at a 

 higher magnification. This gives a faithful idea of the mode of exit of 

 the parasites ; on each side of the pale circle in the mid-lateral region in 

 the mesothorax, there is a larva just beginning to emerge ; at p, another 

 larva is issuing on the ventral surface. At t is the web being spun by 



