ANNULOSA: ARACHNIDA. 



321 



like the other Arachnids, they have the sexes united in the 

 same individual. 



Family 3. Acarida. This family includes the Mites, Ticks, 

 and Water-mites, some of which are parasitic, whilst others 



anychus telarins, one of the 



Fig. 164. Arachnida._ a Pycnogonum littorale ; b Tetr* 

 " Sociable " mites ; c Hydrachna globulus, one of 



are free, and some are even aquatic in their habits. The mouth 

 is formed for suction, or for biting. There is no definite line 



Fig. 165. A, Demodex folltoiloruni, greatly magnified. B, Emydium testudo, one of 

 the Tardzgrada, greatly magnified. C, Sarcoptes scabiei, the Itch-mite, greatly 

 magnified. '-'(' ' 



of demarcation between the unsegmented abdomen and the 

 cephalothorax. 



In the true Acari (fig. 164, b), of which the Cheese-mite may 

 be taken as an example, there are four pairs of legs, adapted 

 for walking, and the mouth is provided with distinct mandibles. 

 Besides the Cheese-mite (A. domesticus), another well-known 

 species is the Acarus destructor, which feeds upon various zoo- 

 logical specimens, and is very annoying to the naturalist. In 

 the Sarcoptes scabiei the cause of the skin-disease known as 

 the " itch " the two anterior pairs of legs are provided with 



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