THE LIFE-HISTORY OF THE BLACK-CURRANT GALL-MITE. 371 
‘occurred several times before it was realized that the dis- 
appearance was not accidental, but that the animals were, in 
fact, leaping. 
As soon as this was suspected, it was easy to verify it by con- 
centrating attention on one individual and using powers which 
allowed the whole of its flight to be followed. The conclusions 
arrived at were these:—After several vain attempts to attach 
itself to a passing insect, a mite would cease to wave its legs, 
remain rigid a moment, and then launch itself forth, torpedo-like, 
into space. The precise mechanism by which this was effected 
could not be determined, but the terminal muscular disc, which 
had been observed to be retractile, was evidently the propelling 
organ. The tail-bristles were at first suspected of taking some 
part in the action, but further observation showed that, by re- 
taining too firm a hold on the bud, they sometimes rendered the 
leap abortive, the mite simply falling backwards with considerable 
impetus instead of darting away. No great distance was covered 
by the leap, the longest measured being four millimetres, or 
about sixteen times the animal’s length. When the mites leaped 
from a bud placed on a microscope-slide they alighted on their 
heads and fell over with the tail-dise most distant from the point 
of departure. 
It was an interesting and suggestive fact that while the mites 
would remain upright with waving legs for several minutes in 
the still air of the laboratory, they could be induced to leap at 
once by blowing upon them with the breath or by means of a 
pipette. It would seem, then, that they first of all try to come 
in contact with a passing insect, and, failing this, take advantage 
of a puff of air to attain their object. 
In view of the extremely doubtful advantage of a blind leap 
into space, the conjecture may be hazarded that the mite thus 
sometimes attains a flying insect which hovers near enough to 
fan it by the beating of its wings. 
Destination of the Migrating Mites. 
The problem of the immediate object of the mites in leaving 
the old buds by crawling, leaping, and adhering to insects next 
demanded a solution. At the height of the migration the new 
buds were already visible and beginning to swell, and the manner 
in which and the extent to which they acquired the disease had 
still to be ascertained. Moreover, the leap into space would 
