180 



PRACTICAL PARASITOLOGY 



with rows of recurved teeth, the size, number and arrangement of 

 which differ in the two sexes; the dorsal surface is smooth. Upon 

 the dorsal aspect of the hypostome are the chelicerae or mandibles. 

 They are surrounded by a sheath which, in the male, is covered with 

 fine transverse lines, but in the female is shagreened. Each mandible 

 consists of a long stem, which is prolonged for a varying distance into 

 the interior of the body, and of a short finger, which bears at its 

 distal end two apophyses, placed externally and internally. The 

 external margin of each is edged with teeth, the number, size and 

 position of which differ, not only in the two apophyses of the same 

 finger, but also, as in the case of the hypostome, in different species 

 and in both sexes. 



Fie. 91. Dermanyssus 

 40 : 1. (After Delafond.) 



hirundinis. 



FIG. 92. Tyroglyphus farince, 

 100:1. (After Berlese.) 



Male. 



Eepresentatives of other families of the Acarina are readily obtain- 

 able. Dermanyssus hirundinis (Herm.) is frequently found in swallows' 

 nests, but should not be sought for during the nesting season ; D. 

 (jallince (de Geer) is found, though more rarely, in henroosts and dove- 

 cots; Lcelaps stabularis is met with in the litter from cowsheds. These 

 three species belong to the family Gamasidce ; they may occasionally 

 attack man. Different species of Tyroglyphidae are found on cheese, 

 jams, dried fruits, mushrooms, smoked foods, dry anatomical prepara- 

 tions, drugs, and other dry organic substances which are in process 

 of slow decomposition. These species may occasionally attack man, 

 though they are more frequently encountered in vessels employed to 

 hold human secretions and excreta. They have an unstriated cuticle 

 and the legs are furnished with leaf-shaped, unpedunculated suckers. 

 They differ in these two points from the parasitic Sarcoptidse, Analgidse, 

 Cytoleichidae, &c., which otherwise they closely resemble. In the 



