ON INDIAN PARASITIC FLIES. 
707 
species on pedicels. The maggots hatch out and penetrate the cater- 
pillars. In some cases the segments of the parasitic maggot’s body 
are furnished with rows of minute spines directed backwards. These 
help progression over the caterpillars skin and are aids to penetration 
also. In the .second .stage of the maggot’s life, having served their 
purpose, the spines for the most part disappear. A very marvel- 
lous adaptation appears in the third or penultimate stage. The pen- 
ultimate stage of many Tachinid maggots presents this strange pecu- 
liarity. During the. two first stages the maggot derives no air from 
the outside. In the third stage it protrudes a pointed posterior end 
through the skin of the caterpillar. The protruded end becomes 
highly chitiniscd from exposure to the air and ends in a pointed tube 
in the base of which lie the posterior stigmata. Through this pro- 
truded tube the maggot obtains air. The fourth and last stage of 
these maggots is passed living free inside the hosts. The cast skins 
of the penultimate stage remain fixed in their place protruding through 
the caterpillar’s skin. A few species remain as last-stage maggots 
within the chitinised cast skin and transform to pupm inside 
the caterpillar skin. Most Tachinids pupate outside the host and 
the exit is fatal to the host. 
2. Leaf-oviposition. The suggestion that the parasitic maggot 
could obtain entrance into the host by the egg in which it is enclosed 
being swallowed by the caterpillar, was received with incredulity 
when originally put forward. The facts are now well established. 
The eggs are swallowed by the caterpillars and hatch within their 
alimentary canal. In such cases the eggs are minute, perhaps not a 
fiftieth part of the usual size, though the flies laying them may be 
larger than the average size. The piece of leaf swallowed by the 
caterpillars may be six or eight times the size of one of those eggs. 
Where a fly produces minute eggs it is certain that when matured 
they will be black and highly chitinised. They are intended to 
stand exposure and swallowing. Probably such eggs when depo- 
sited on leaves can retain their vitality for a long while. Probably 
also they are not laid until the embryo is well developed ; the diges- 
tive juices and the conditions in the alimentary canal act on the 
chitin, weaken the shell and release the maggot. It is certain that 
somehow the egg must hatch within a few hours of being swallowed 
else it would pass through the gut of the caterpillar and perish. A 
very small egg cannot have a thick chorion and is therefore provided 
with a chitinised thin one which withstands atmospheric conditions- 
better than an unchitinised thick one. Some eggs are protected by 
a reticulated surface which possibly preserves them from injury in 
the swallowing. Thus the history of the species can be read from' 
the uterine eggs dissected from the female Tachinid. 
3. Supracutaneous host-larviposition . This brings us to anothei 
