2 28 ARACHNOIDEA. 



CASE sites; the third, Tyroglyphid^, not parasitic; the fourth, Sarcop- 

 tid^e, are burrowers in or parasitic on the skin of mammals ; the 

 Dermaleichidse are feeders on fur and feathers of hving animals ; 

 and the Phytoptidse browsers on the skin of buds and leaves, pro- 

 ducing excrescences like galls on the latter. With scarcely an 

 exception, all of the first section have a smooth skin not marked 

 by minute strise, lines or wrinkles. Of the second, on the other 

 hand, all have the skin marked by fine strise or lines like wrinkles, 

 the lines being distributed after a definite pattern, differing in 

 each species. In the former the legs are usually tenninated by a 

 single claw, more or less distinct, and although in many species 

 this is accompanied by a sucker or vesicle, it is usually small, and 

 generally surrounds the claw, like a sleeve ; while in the latter the 

 suckers, w?th rare exceptions, are present as a prominent feature, 

 while claws are either absent or only slightly developed. 



Sub-Family Hypoderid^. 



Parasitic sub-cutaneous mites living between the skin and the 

 muscle of certain birds. They are oblong oval, almost trans- 

 parent bags, with the two anterior and two posterior pairs of legs 

 placed a long way from each other ; the claws of the tarsi seem to 

 be two fine hairs, and we do not think that the parts of the mouth 

 have been deciphered. 



Montague seems to have been the first to notice these creatures ; 

 at least, the species named by him Cellularia bassani, which lives 

 in the air cells under the skin of the solan goose (Sula bassana), 

 must have been one of this genus. Nitzsch next observed the 

 same species, which he named Sarcoptes subcutaneus. Then, in 

 1843, Miescher described two found in the common swift (Cyp- 

 selus apus), one in the bronchial tubes, (which, notwithstanding 

 that Erichson, from the description, thinks must have been a Der- 

 maleichus, from the habitat most probably belongs to this group), 

 and another from the air tubes and lungs of the Butcher-bird 

 (Lanius Excubitor) in immense quantity. 



