Vinegar-fly (Drosophila funebris). 301 
protruded, and become functional. Full-grown larve bite 
their way to the surface of the leaf-stalk, crawl through 
the aperture, fall to the ground, and there pupate. In the 
swedes that I kept in the laboratory a few pupz were 
found protruding from the ends of the burrows in the leaf- 
stalk ; this was probably accidental and due to artificial 
conditions, for the swedes in the field had no projecting 
upe. 
¥ The Pupa of D. fenestrarum—The pupa, although 
smaller, exhibits the same structure as that of D. funebris. 
Larve were collected at the end of October; they soon 
pupated, and in the course of ten or twelve days several 
flies emerged. In summer the duration of the pupal stage 
would be still shorter. The flies seem to persist late in 
the year; on November 24th a living one was captured 
upon swedes. 
The larve, as it has been stated, mine the leaf-stalks. 
A mine usually runs up the vascular tissue, extending 
from the leaf-base for a considerable distance up the leaf- 
stalk, The walls of the burrows exhibit signs of decay. 
Professor Potter of Newcastle-upon-Tyne has given 
attention to the decaying agents in the swede and turnip,* 
and has shown that it is due to bacteria. But these 
bacteria are “powerless to set up decay unless placed in 
contact with the parenchymatous cells of the cortex.” 
Although many other living things, such as caterpillars, 
slugs and snails, may be chief agents in giving the start to 
the decaying bacteria, the mining habits of such larve as 
Drosophila would provide the bactertum with a ready 
means of access to the underlying parts. As the larva 
eats its way up a leaf-stalk it gives access to bacteria, and 
may carry bacteria along with it as it travels from infected 
to sound parts. The tissues adjoining the burrows turn 
brown and decay, and in the end the whole leaf may 
shrivel and fall off. 
In much-decayed swede-crowns I have found blow-fly 
larvee feeding. 
In conclusion, I wish to tender my sincere thanks to 
Professor Miall for the interest he has shown and for the 
help and encouragement he has given me during the course 
of this inquiry. 
* Potter (1899 and 1903). 
