372 
Parasites of Common Flies 
ranged from 2 to 9 from each puparium. Some of the jars in which the fly 
puparia were kept were covered with cloth in January 1916 and in these no 
chalcids were found. Consequently the infection occurred in the spring of 
1916. All these chalcids occurred in puparia parasitised by A. manducator, but 
it is probable that at the time infection took place no normal puparia were 
present, the flies having already emerged. Experimentally D. cavus oviposits 
in the normal puparia of many common flies, including M. stabulans and P. 
greenlandica. The process is very similar to that which occurs in the case of 
M. acasta. D. cavus in emerging makes a round opening much larger than 
that made by M. acasta, which may be situated in any part of the puparium. 
Several experiments were carried out in which females together with males 
of D. cavus were confined in tubes with fly puparia. In one 15 puparia were 
used. In four of these puparia 5 A and 45 $ emerged; one contained dead 
adults and 10 dry fly remains. A single fertilised female was confined with a 
different puparium on consecutive days. From six of these 6 and 50 $ 
emerged. This parasite therefore seems to be less prolific than M. acasta. 
In another experiment 16 of the chalcids, males and females, were confined 
in one tube with eight fresh fly puparia. The parents were all dead by the 
seventeenth day, and the new generation began to emerge on the thirty-sixth 
day. Altogether 20 $ and 63 $ emerged, giving a mean of 2 $ and 8 $ for each 
puparium. One puparium contained 2 <$ and 12 $, another 5 and 9 $ and 
another 4 $ and 11 $. All the puparia were parasitised. 
Nasonia brevicornis. 
This chalcid was first obtained from puparia collected in the summer of 
1916, and emerged at the end of April 1917. From 16 puparia, unparasitised by 
A. manducator, 14 and 167 $ emerged, a mean of 11 chalcids to each infected 
puparium. Puparia collected in the autumn of 1916 and kept outside yielded in 
May 1917 38 and 369 ?. Some of these autumn puparia had been parasitised 
by A. manducator. The proportion of males to females was therefore about 1 to 
10 in each instance. Some of these autumn puparia remained intact, and were 
dissected in March 1918. Of these 28 were found to contain living chalcid 
larvae and were kept in tubes in a warm room. Nineteen of these 28 showed 
infection with A. manducator. Adult N. brevicornis, 11 3 and 48 $, emerged in 
May 1918, a year and a half after the puparia were collected. 
Both the males and females show great variations in size, some of the 
former being very small and many of the latter very large. The males have 
very short wings and are unable to fly. Unlike the males of M . acasta they 
emerge from the fly puparia, and run rapidly amongst the earth and debris 
and are difficult to find and catch. As in the case of D. cavus the hole through 
which the chalcids emerge may be situated in any part of the puparium. 
Ten females confined in a tube on April 30, 1917, with 19 puparia were all 
dead in 13 days. From 16 of these puparia 24 £ and 156 $ emerged between 
the twenty-fourth and twenty-ninth days from the commencement of the 
