168 
Dacnusa areolaris Nees, etc. 
under the epidermis. The actual insertion of the egg apparently presented 
some difficulties, and the ovipositor was half inserted and withdrawn many 
times. Occasionally two parasites attacked the same larva, and jostled and 
thrust each other aside in their efforts to oviposit. If the blister was cut open, 
the Braconid would sometimes slip inside it, but in such cases she ignored 
the object of her search which lay exposed before her, and ran out again 
immediately to probe for it through the epidermis. 
Larvae which had already been parasitised were never attacked, and in 
the considerable quantity of material examined two parasites were never found 
in the same host. Epiparasitism 1 (double infestation) does not seem to occur 
in this species. 
The egg, when first laid, is an oval body somewhat pointed at the anterior 
end (Fig. 1); but, as segmentation proceeds, it increases in size and becomes 
more spherical. It lies freely in the haemocoele, generally in the posterior 
third of the body, but occasionally may be found near the head. The material 
available was insufficient for the study of the embryology of the parasite. 
The earliest larval stage, which appeared in every larva found parasitised in 
the field, is that shown in Fig. 2. The larva, transparent and vermiform, lies 
slightly curved to the ventral side, in the cavity of a hollow sphere of flattened 
cells, the u trophic membrane,” which completely envelopes it. The body 
consists of thirteen segments, each of which from the second to the twelfth 
bears dorsally a few short spines. The thirteenth segment, which is blunt and 
rounded, is provided with a semicircle of stouter setae, arranged fanwise round 
the anus. The larva is able to move about within the trophic membrane. The 
cells of the latter, though polygonal in surface view, are flattened and crescentic 
in section, and towards the end of embryonic development their nuclei appear 
in various stages of degeneration. This cellular sphere is enclosed in a fine 
structureless membrane. 
In this condition the parasite remains until the host larva, is fully fed 
and falls from the leaf. Examples examined twelve hours after this event 
show some increase in the size of the parasite, which half fills the cavity of 
the membrane. The latter becomes attenuated and is pierced by the dorsal 
and caudal spines. It ultimately ruptures in the region of the mouth of the 
parasite, which now begins to feed, and the mesenteron, filled with ingested 
matter, is clearly visible through the transparent tissues. 
About 36 hours after the host has formed its puparium, the parasite throws 
off the trophic membrane, and with it the first larval skin, both of which soon 
disappear among the surrounding histolysed tissues. 
In the succeeding stages the parasite larva is a semi-transparent, smooth, 
apodous form, slightly curved to the ventral side, and without appendages. 
As it feeds it increases rapidly in size, and, about a week after the first moult, 
having demolished the viscera of the Phytomyzid, it comes forth from the 
empty skin and lies free within the puparium. 
1 The writer first suggested and defined this term (1922) in Proc. Camb. Philos. Soc. xxi. 27. 
