4 BRITISH TYROGLYPHID^. 



followers than causers of decay; although Meguin, 

 their discoverer, did not take that view of the matter ; 

 they wade half immersed in the thin film of liquid 

 which covers the surface of mushrooms and many 

 other fleshy vegetable substances when in a state of 

 incipient decay ; which they probably hasten consider- 

 ably by cutting the cells as they advance with alternate 

 strokes of their serrated mandibles ; which are different 

 from those of any other genus in the family, and 

 driving the stream of cell-contents into their mouths 

 by regular beats of the flagella borne by their excep- 

 tional palpi ; some of their species live in the exuded 

 sap of forest trees, such as the elm, etc., in places where 

 the bark has split. The members of the small genus 

 Hericia have a similar habitat, but not by any means 

 similar mouth organs; there is not any reason to 

 suppose that either the one or the other does any 

 substantial damage to the trees. Hixtiocj aster corticalis 

 is also found on succulent stems, but here, again, it is 

 when they are dying that the acarus attacks them. 



There are but few species of Tyroglyphidae which 

 are parasitic in the adult condition. Grlycyphayux 

 (Dermacarus) sciurinus may be looked upon as one ; it 

 is found adult in considerable numbers on the squirrel ; 

 but, as far as my own experience goes, in greater 

 numbers in its nest. Glycyphagus crameri, G. platy- 

 gaster, and 6r. dispar are all found in moles' nests, but 

 I have not ever been able to find either of them in the 

 adult condition on the mole itself ; there is probably 

 also a species associated with the nests of field mice, 

 but little is known about it. The larvse and ordinary 

 nymphs are not any more parasitic than the adults ; it 

 is only in the hypopial stage, where there is one, that 

 a sort of parasitism exists, but even there the Hypopus 

 only seeks conveyance and transfer to fresh localities 

 from its host; it does not seek nourishment from it 

 nor live upon it permanently. If a Hypopus be 

 parasitic upon its host, then a horseman is almost 

 equally so upon his horse. 



