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X 
CHEESE-MITES AND SOME OTHER MITES. 
By John Hopkinson, E.L.S., E.G.S., E.R.M.S., etc. 
Read at Watford, 3rd February, 1904. 
The Acari, popularly known as cheese-mites and scientifically 
as the Tyroglyphidae, are a small family, having very few genera 
and not many species. They are of small size, very few species 
reaching the thirtieth of an inch in length, and only one ever 
exceeding one-twentieth of an inch. But they make up for 
fewness of species and smallness of size by the countless numbers 
in which some of their species occur. 
They are exceedingly destructive to dried or preserved food 
of many kinds, and also to drugs which consist of animal or of 
vegetable matter. They do not usually attack living plants or 
animals in a state of health, except bulbs and tubers, hut when 
such a plant as a fungus, especially if fleshy or gelatinous, shows 
the first signs of decay, it is often attacked by mites which hasten 
its decomposition. Hay is very liable to attack, and so is flour, 
and dried fruits and sweet wines often suffer much. Samples of 
an infested hay-stack, taken at random, have been found to consist 
as much of mites as of hay. 
All the Acarina undergo a metamorphosis, but in the cheese-mites 
and their allies there is one stage which does not appear to be 
certainly passed through in any other family of mites, or indeed 
in any other creatures, the one or two exceptions which have been 
adduced amongst the Acarina being very doubtful. This is a con¬ 
dition of fasting and clinging undergone in order to secure the 
wide dispersal of the species in which it occurs, and it is of so 
much biological interest and economic importance that I think 
a few minutes may well be devoted to its consideration. It is 
called the “hypopial stage”; and to discover what this stage 
actually is has been reserved for the patient investigation of 
Mr. Albert D. Michael. 
The Tyroglyphidae, like almost all other Acari, pass through 
four principal stages—the ovum, the larva, the nymph, and the 
imago. The eggs are usually oval, smooth, and white or light- 
coloured, and their cuticle cannot be called a shell, like that of 
many Acari, being soft and capable of expansion. The larva is 
hexapod, the nymph and imago are octopod, the fourth pair of 
their eight legs being wanting in the larva. After a short inert 
period the larva casts its skin and becomes a nymph, the first 
ecdysis which the creature undergoes. There is usually a great 
resemblance between the nymph and the earlier and later stages, 
the. larva and the imago. The nymphal stage is the growing 
period, it is the period between the first and the last ecdysis, and 
within it occurs the second ecdysis by which the “ first nymph” 
becomes the “ second nymph,” a period of inertness or torpidity 
