708 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXVIII. 
phase of Tachinid parasitism but the leap from reproduction by living 
larvae is not so abrupt as it may seem. There are species of Tachi- 
nidce in process of transition. Female Tachinids of certain species 
may deposit eggs almost undeveloped, or at any stage of the develop- 
ment of the embryo, or may even perhaps deposit living maggots. 
When the larva is deposited on the skin of the caterpillar it is exposed 
to much the same danger as an egg ; it may be accidentally or pur- 
posely removed by the caterpillar and if the host moults before the 
maggot has managed to penetrate this is fatal. 
4. Subentaneom host-larviposiiion. Another step forward is at- 
tained if the parasitic maggot can be immediately introduced beneath 
the host’s skin. The females of those Tachinids which have attained 
this higher grade of efficiency are furnished with a long curved sheath 
which tapers down to a point and is microscopically fine and sharp. 
The ovijDositor fits into the base of this organ and wdth this 
organ the female Tachinid punctures the caterpillar’s skin at the 
moment when the living maggot is being extruded. Until Townsend 
and his assistants worked at this group (1908) the habit of introducing 
the living maggot within the skin of the host was never suspected in 
the Tachinidee. 
5. Leaf-larviposition. It is unexpected to discover that Tachinid 
parasitism reaches, apparently, the highest efficiency in those forms 
which deposit their maggots on leaves to wait the passmg by of a 
chance host. The maggots, in a fashion wonderful to relate, are 
securely attached to the surface of the leaf at the moment of biidh 
by a membranous cup-shaped case which holds the posterior end of 
their bodies. The maggot can reach out in all directions and moves 
constantly on feeling the proximity of a host. When midisturbed it 
lies at length on the leaf but on being touched it becomes excitedly 
active seeking to attach itself to the expected host. No sooner does 
it lay hold of a caterpillar than it is torn from the cup-shaped attach- 
ment by the motion of the caterpillar and its own exertions. 
It would be thought perhaps that the chances of parasite and host 
meeting under such conditions were very remote. But this is not the 
case, for the Tachinid female selects leaves and stems where cater- 
pillars have already crawled and usually deposits a maggot where 
a silken thread has been left by a caterpillar. Possibly the sense of 
smell guides the flies in selecting these silken threads. In such a 
case, where the caterpillar follows the thread back, it is sure to pick 
up the maggot on the way. 
A second- advantage is gained by this habit in the greater certainty 
with which a maggot can become attached to a caterpillar especially 
if one of a hairy sort. Being placed where the caterpillar will pass 
over it, the maggot can attach itself with greater ease to the under parts 
where hairs are sparse and short. If the female Tachinid tried to 
