MITES. 147 



however, he has had no followers. From the very valuable 

 discoveries lately made by M. Duges, an indefatigable French 

 naturalist, it has been proved that they undergo metamor- 

 phoses, consisting in some groups of an increase in an addi- 

 tional pair of legs, whereby one of the sections proposed 

 in the group by Latreille and Hermann (Trombides hexa- 

 podes) is found to consist only of insects in an imperfect 

 state, whilst in others the change of form is complete. This 

 is especially the case in the water mites, the larvae of which 

 have a very large head and six legs : the pupse are inactive, 

 attaching themselves by a single pair of very short legs to 

 the bodies of other aquatic insects, and being composed as it 

 were of an oval bag with a narrow neck ; the insect in this 

 state having been formed by M. V. Audouin into the genus 

 Achlysia, and being specifically named A. Dytici, from taking 

 up its residence beneath the elytra of the great w r ater-beetle 

 (Dyticus marginalis) ; they also attach themselves to the 

 slender filaments composing the tails of the water-scorpions 

 (Nepa and Ranatra). 



In the recent memoir of M. Duges the order is divisible 

 into the following seven families : namely, 1. Trombidiei ; 

 2. Hydrachnei; 3. Gamasei; 4. Ixodeij 5. Acarei; 6. Bdellei; 

 /. Oribatei. 



Amongst these insects the cheese mite (Acarus domesticus) 

 is one of the most common species, and which is so abun- 

 dantly met with in dry cheese, flour, and meal. They are 

 clothed with long hair, and their feet are armed with strong 

 hooks, enabling them to retain firm hold of the situation in 

 which they abound. The females are oviparous. 



Another species belonging to the restricted genus Acarus 

 has attracted much attention, from being the cause of a dis- 

 gusting disease, named Acariasis, to which unclean persons 

 are occasionally subject. It is found in the vesicles of the 

 itch, and has recently been the subject of numerous micro- 



