D. Keilin 
437 
the length of the larva, will be found coiled around it and attached by one end 
to its anus. This tube, which is the peritrophic membrane, is fairly resistant 
and keeps the excrement separated from the putrefying snail which is the food 
of the larva. 
The larva, when full grown, leaves the shell, penetrates into the earth, and 
by the next day it becomes a pupa from which about 14 days later the adult 
emerges. 
I endeavoured to find out the duration of each stage of the lafrval life but 
did not succeed because it was impossible to discover by any external signs 
whether or not the snail was parasitised. Had I found the Church Rate Walk 
snails at a sufficiently early date 1 would have dissected out the eggs and 
different larval stages from parasitised snails and inserted these in the un¬ 
parasitised ones; but, by the time I discovered this apparently immune 
colony, the parasite was too far advanced in its development. I can only say 
that the development from egg to pupa is completed in about 15 days so that 
the whole life-cycle occupies about a month. I found the parasitised snails 
during June to September, but, as in June the snails contained some advanced 
larvae, it is probable that the life-cycle begins in May. The rapidity of the 
larval development indicates that Melinda probably passes through three 
generations in the year. The species hibernates in the pupal stage since I have 
found pupae during the whole year. 
I mentioned previously that a snail may contain two or three larvae in 
different stages of development but only one of these larvae succeeds in com¬ 
pleting its life-cycle. The others are always killed; the surviving larvae biting 
the others and possibly sucking them by accident; the brown scar of the bite 
can be seen on the deflated skins of dead larvae. 
The parasitised snail cannot rid itself of the parasite. I never found a 
Melinda larva mechanically expelled from the snail nor phagocytised in the 
host’s body as was often the case with Pollenia rudis in the earthworm (cf. 
Keilin, 1915 a, pp. 50-57). 
Attempts to obtain eggs under artificial conditions were unsuccessful. A 
large number of males and females of Melinda , bred out from the snails and 
enclosed in a muslin cage, were fed with sugar and honey which they readily 
took. At intervals I dissected females but in no case did I find the ovaries 
developed or spermatozoa in the spermathecae. In all the females the fat body 
was largely developed, and this condition persisted from August until Decem¬ 
ber by which time I had exhausted my material. PI. XXV, Fig. 16, shows 
the state of the internal genital organs of one of these females. 
( c) Hymenoptera hyperparasites of M. cognata. 
As parasites of Melinda cognata Meig. J can only mention two lchneu- 
monids, which were kindly identified by Mr Claude Morley as At ract odes exit is 
Hal. and Exolytus petiolarius Thomson. Very little is known of the life-history 
of these Hymenoptera. In Morley’s book on British Ichneumonids there is 
