120 MAUD D. HAVILAND 
The fourth instar lasts between two and three days. Ly go- 
cerus does not spin silk, but pupates within the cocoon pre- 
viously woven by the Aphidius. Just before metamorphosis, 
the mid-gut opens into the hind-gut, and the contents are 
voided. The larva is active, and by its movements the frass, 
together with the now empty skin of the host, are welded into 
TExt-Fic. 18. 
Vertical section through the developing genital armature of a male 
larva of the fourth instar. x 350. de. 7. imaginal disk of forcipes. 
ct.=cuticle hp.=hypoderm. 
a compact, moist pellet at the ventral side of the body. The 
frass of the Proctotrypid, Chalcid, and Cynipid parasites of 
Aphidius ean readily be distinguished from one another, 
for that of Lygocerus is invariably a single black mass, 
whereas that of the Chalcidae and Cynipidae consists of several 
pieces of a different form and colour. 
Moutts. 
The determination given of the number of moults, and the 
duration of the instars, is based on the examination of many in- 
dividuals of different ages, and may be somewhat arbitrary ; 
but it was the only practicable method to employ, since it 
