SPINNING MITES. 95 



CASE have often some peculiarity on their second pair of legs, such as 

 being much enlarged or provided with hooks, &c. 



The Ticks, or Ixodidae, are at once known by their leathery 

 abdomen, by having a sort of shield on the back, immediately 

 behind the head, and by their fastening on warm-blooded animals 

 and sucking their blood, for which they have a specialized mouth- 

 piece. 



The Halacarldse are marine, and the Oribatidse have a chitonous 

 skin, like beetles. 



The Acaridae are semi-transparent, and nearly colourless. The 

 cheese mite section maybe distinguished by having the skin smooth, 

 and the tarsi usually terminated by a single claw with or without 

 a sucker, which when present is not conspicuous. In the Sarcop- 

 tidse the sucker is conspicuously the chief organ of locomotion, 

 and the skin is always covered with more or less transverse lines 

 or wrinkles. The Phytoptidae also have the skin wrinkled, but 

 only four legs, the two posterior pairs being replaced by bristles. 

 They are excessively minute, and only found in buds or leaf-galls. 



Family TROMBIDIIN.^. 

 Besides the general aspect and habits which we have already 

 noticed, this group is to be distinguished by its palpi, which have 



I'alpi of Tronibidium fuliginosum. Typical palpus of Trombidium. Copied 



from Dug6s. 



generally the second joint longest, and the last bearing an append- 

 age which with it serves to act as finger and thumb ; sometimes it 

 is like a claw, and at others is diminished to a hair, but is almost 

 always present in some form, and usually easily enough dis- 

 tinguishable. It is however not absolutely confined to this family, 

 similar appendages sometimes reappearing in the Gamasidae. 



