706 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXV Hi. 
almost solely iu flies with pedestrian habits and he concludes that 
the machrochaelce are organs of orientation which fulfil much the 
same function as a cat’s vibrissae or whiskers. If it be the 
truth that the bristles on the Tachinid and other flies are connected 
with pedestrian habits, it is worth noticing in confirmation that in 
another utterly different animal, namely the three-toed Sloth, whose 
habits are the reverse of pedestrian, facial vibrissae are absent. 
There can be little doubt that parasitism in the Tachinidce is fairly 
recent and not nearly so effective and well evolved as, for instance, 
in the parasitic Hymenoptera with almost similar habits. Unlike 
most of the parasitic Hymenoptera, these Dipterous parasites do not 
usually confine themselves to one particular host. By far the largest 
number of species are parasitic on lepidopterous larvae. The lives 
of some 400 species have been more or less studied. About 70 
are parasitic on Hymenoptera. Then follow as hosts ; Coleoptera ; 
Orthoptcra ; Hemiptera ; and other Diptera in diminishing numbers. 
The precise adjustment of perfect parasitism has not yet been 
attained by these flies and they make two frequent blunders with 
disastrous results to their offspring . The first consists in laying 
eggs on a caterpillar which is about to moult ; the second, in laying 
eggs on a caterpillar which has been already parasitized, with the 
result that some or all of the young Tachinids perish of starvation. 
This points to the comparatively recent adoption of this mode of 
life. Yet when all is said the Tachinid flies are a successful family. 
To secure successful parasitism five forms of reproductive habit 
have been evolved in the Tachinidce. They are thus summarized 
by Townsend 
1. Host-oviposition. 
2. Leaf-oviposition. 
3. Supracutaneous host-larviposifcion. 
4. Subcutaneous host-larviposition. 
5. Leaf-larviposition. 
These five forms of reproduction are arranged above in order of 
probable antiquity. The placing of the egg upon the host is thought 
to be the most primitive, and the placing of the larva on a leaf, where 
the host will pass, appears to be the most recent stage. From the 
commonsense view of the habits of these flies this seems natural ; 
and it is also confirmed by a study of the external characters of the 
flies.* A few words may be added on each of these five methods 
of reproduction. 
]. Host-oviposition. The eggs are laid by the female Tachinid 
on the caterpillars. The eggs are usually thin shelled and in some 
* C. H. T. Townsend (1908) “A record of results from rearines and di.«sections 
of Tachinidae.” U. S. Dept. Agriculture. Bureau of Entomology. Tech. Series 
No. 12 Pt. VI. pp. 95-118. 
