430 Miscellaneous. 



and bears beneath the abdomen an adherent apparatus composed of 

 five pairs of suckers. By placing it in suitable conditions we have 

 seen this Hypopus also resume its original form of Tyroglyphus. 



These observations completely solve the problem of the dissemi- 

 nation of the detriticolous Acarina. Every one who studies the 

 animals which live in decomposing substances must have often asked 

 himself how those legions of Acarina which swarm and appear in 

 myriads in them in so short a time get there, and what becomes 

 of them when their work of destruction is completed, and the material 

 in which they swarmed, being reduced to the state of a dry powder, 

 no longer offers them any nourishment. These little creatures 

 have not the aid of wings to enable them to fly from places desolated 

 by famine ; nor have they the activity of the ants, which enables 

 those insects to migrate and make long journeys. They have soft 

 integuments, which afford them but little protection against external 

 influences and the voracity of their numerous enemies ; exposure to 

 the sun kills them ; and thewoodlice destroy them in great quantities ; 

 their eggs, which are comparatively large, are not to be met with 

 in the dust of the air in company with the germs of moulds and In- 

 fusoria ; and, lastly, they do not enjoy the faculty of reviving after 

 desiccation, like the AnguiUulce, Rotifera, and bear-animalcules. 

 One can easily understand how they came to furnish a principal 

 argument in favour of the theory of spontaneous generation. Now 

 this is what takes place in a colony of Tyroglyphi when the privation 

 of food seems to devote it to certain destruction. All the adult 

 and old individuals, as well as the young hexapod larvae, die and 

 strew the soil with their bodies ; but the adolescent individuals (the 

 octopod nymphs) are preserved : they change their form, acquire a 

 cuirass, a true travelling garb, which acts as a complete disguise, 

 but which at the same time protects them from external influences ; 

 moreover they acquire an adhesive apparatus, by means of which 

 they can attach themselves firmly to any creatures that come 

 within their reach — flies, spiders, myriopods, insects of all kinds, and 

 even quadrupeds, which, like regular omnibuses, transport them 

 where they could not go themselves. If the place where the vehicle 

 stops is suitable, if it is by a fresh fungus or a mass of rubbish in 

 decomposition, the little mite quits the animal that bears it, as well 

 as its Hypopus- form, and becomes a Tyroglyphus, such as it was 

 before. Under the influence of abundant food it grows rapidly, 

 becomes adult and sexual, copulates, and in less than forty-eight 

 hours the colony is founded afresh. That is the function of the 

 Hypopus. 



The conclusion to be drawn from my observations is that the 

 genera Hypopus, Homopus, and Trichodactylus, and the numerous 

 species which have been established as subdivisions of those genera, 

 must be struck out of our zoological nomenclature. The word 

 Hypopus may be retained, but only as a common name serving to 

 designate the curious cuirassed, heteromorphous, and adventitious 

 nymph of the Tyroglyphi, whose office is the preservation and dis- 

 semination of the species to which it belongs. — Oomptes Bendus. 

 August 18, 1873, p. 492. 



