AND SOME OTHER MITES. 
71 
Tyroglyphus , to enable it to endure the journey from one fungus, 
etc., to another, which would sooner or later become necessary 
from the drying or destruction of the first fungus.” In 1881 
Berlese published a paper in which he agreed in the main with 
Megnin, and added the apparently correct observation that 
u Hypopus does not take any nourishment.” 
Such was the state of our knowledge when Mr. Michael, in 
1884, published the results of his observations in a paper read 
before the Linnean Society of London. 
Mr. Michael commenced his experiments by breeding the cheese- 
mites, Tyroglyphus siro and T. longior, in small glass cages, but 
only with difficulty succeeded in getting the hypopial nymph of 
one of these species, T. longior. In 1881 he found that there was 
no difficulty in obtaining and rearing the hypopus of another mite, 
Tyroglyphus mycophagus, and the conclusions he drew from his 
experiments were that from the cast skin of the young nymph, on 
its first ecdysis, the second in the life of the individual, there some¬ 
times emerges a hypopus, though usually a second nymph; that 
this hypopus may be either a male or a female; that adverse 
circumstances, such as drought, do not tend to increase the 
production of hypopi; and that by an ecdysis, preceded by a period 
of inertness, the hypopus becomes again a nymph. The hypopial 
stage is, in fact, an occasional one in the life-history of certain 
species of Tyroglyphus and of some allied genera in which they can 
withstand great changes of temperature and absence of moisture, 
and do not require food, and during which they cling to insects or 
other creatures for the sake of conveyance in order to secure the 
wide distribution of the species. 
There are two or three different kinds of hypopus; in two they, 
are protected by a chitinous cuticle; in one of these they cling to 
the smooth surfaces of insects, etc., by means of suckers, in the 
other they attach themselves to the hairs of mammals, on which 
alone they are found, by means of a short longitudinal furrow in 
which the hair lies and is firmly secured by clasping organs on 
either side of the furrow, this type of hypopus being termed 
homopial. The third type of hypopus, which is termed tricho- 
tarsial, is a nymph without a chitinous carapace, but provided, as in 
the true hypopi, with suckers by which it becomes attached to 
wild bees of the genus Osmia , etc. As no other nymphal stage is 
known in the mites which assume this form, it is doubtful whether 
the trichotarsial condition should be considered as truly hypopial, 
but Mr. Michael inclines to the belief that it is so. Hypopi occur 
in. immense numbers, fifty on one ant being a small number, 
a single ant in a badly-infested nest sometimes carrying thousands 
upon it and dying under its burden. 
It should here be mentioned that Mr. Michael has conclusively 
proved that hypopi are not parasites, as they were at one time 
supposed to be, the death of the ant under these conditions being 
due to its inability to clean itself with the comb with which its 
front legs are provided, and to the lethargy into which it falls. 
