206 BRITISH TYROGLYPHID^;. 



H. rostro-serratum, and are doubtless the chief, if not 

 almost the only means of distribution of the species ; 

 it is sometimes astonishing after keeping material 

 infested with H. rostro-serratum under observation for 

 some time, under favourable conditions of life, to see the 

 immense numbers in which the Hypopi will suddenly 

 appear. In this genus the Hypopi are apt to have 

 rather long thin legs for that stage, and have a mode 

 of stretching out the two anterior pairs which is 

 characteristic. 



Habitat, etc. As before stated, Megnin originally 

 found the first species of this genus immersed in the 

 thin film of liquid which covers decaying mushrooms, 

 but they are not in any way confined to mushrooms, 

 almost any sort of thick fleshy vegetable matter in 

 a state of incipient decay is acceptable. I found 

 H. pyriforme in the exuded sap of beech trees. 

 Kramer found H. pulchrum in a somewhat similar 

 situation. The Italian acarologists found H. fi.mc- 

 tarium and H. phyllothrichum in dung-heaps ; and 

 most other recorded species have been found on decay- 

 ing vegetable matter. There is one known remarkable 

 exception which was disclosed by the highly interesting 

 investigations of Jensen, quoted in the synonymy at 

 the head of this genus. The Danish naturalist found 

 his species, H. Berghi, in the egg-capsule of the horse- 

 leech (Aulastoma gulo). In 1863, Leuckart described 

 how this creature laid its eggs in a capsule which it 

 buried in the banks of the stream or pond which it 

 inhabited. In 1885, Bergh investigated and described 

 the somewhat complex metamorphoses which the 

 leech larva undergoes within the capsule; he also 

 stated that he found Acari within the capsule. Jensen, 

 in 1895, carefully traced the life-history of the mite, 

 which he found was a Histiostoma. It appears from 

 his researches that from the egg of the Acarus, within 

 the capsule, emerges the usual hexapod larva; which 

 soon changes its skin and becomes an octapod nymph, 

 which gradually devours the larval leech and all the 



