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Transactions of the Society. 
produce a Hypopus instead of an ordinary Tyroglyphas ; but Hypopus 
never contained any eggs. Again the deduction seemed clear, and 
Claparede announced that Hypopus was the male of Tyroglyphus. 
But Bobin and Fumose had found the Tyroglyphus as well as 
Claparede. Of course neither knew of the other’s study, but the 
French paper appeared just before the Swiss, and Kobin and Fumose 
had found the male, which is very like the female. In 1873 Megnin 
took up the study and came very near the truth indeed ; he experi- 
mented on Tyroglyphus mycophagus and another species, both found 
in great numbers on mushrooms; he bred his creatures in cases, 
supplying them with pieces of fresh mushrooms from time to time ; 
he found that when the mushrooms and cages got dry the Tyroglyphi 
disappeared, but were replaced by swarms of Hypopi ; when fresh 
moist mushroom was added the Hypopi were again replaced by 
Tyroglyphi. Megnin concluded that when from the dryness of the 
atmosphere or other unfavourable circumstances the nymphs of Tyro- 
glyphus were unable to live, they had the power of turning into 
Hypopi , which could support drought, &c., and of thus passing the 
period until the conditions had again become favourable. In 1876 
our countryman Andrew Murray contributed a suggestion. Dujardin 
had seen the creature with chelate mandibles inside the Hypopus, 
Claparede and Megnin had seen the Hypopus inside the other. 
Murray suggested that what Dujardin supposed to be inside was 
really underneath and seen through, and that Hypopus was a ferocious 
creature which attacked other mites from below, ate its way in, and 
then devoured its host, leaving only the skin. The absence of mouth- 
organs in Hypopus did not seem to trouble Murray. Between 1882 
and 1884, 1 myself conducted a series of experiments with a view to 
settling the question; it would take far too long to detail these 
experiments, but I found that Hypopus was undoubtedly a stage in 
the life-history of Tyroglyphus , and that every small fly and beetle 
which emerged from a hot-bed, where the conditions were particularly 
favourable to Tijroglyphus life, and where that creature swarmed, was 
laden with Hypopi, and that in my cells the more favourable the 
conditions were the more Hypopi 1 got ; but that, undoubtedly, when 
desiccation commenced the Tyroglyphi died off rapidly, while the 
Hypopi continued to live for a considerable time. I came to the con- 
clusion that the Hypopal condition is a stage in the life-history of 
the nymph of Tyroglyphus, occupying the period between two 
ecdyses, generally the second and third, that it was not confined to 
either sex and did not occur in the life-history of every individual, 
but only of a moderate proportion, and that it was a provision of 
nature for ensuring the distribution of the species by enabling its 
members to cling to passing insects such as flies, bees, &c., and to 
support the exposure to sun and drought, which they would have to 
suffer before arriving at fresh favourable localities, and which would 
assuredly kill Tyroglyphidae in any other stage. This view is now, I 
think, generally accepted ; and it is satisfactory to find that it has 
