254 EVENINGS AT THE MICROSCOPE 



among the sub-aquatic vegetation, bright-colored Mites; 

 sometimes rich velvety green, sometimes purple, but more 

 commonly brilliant scarlet; often curiously marked with 

 sinuous patterns or spots of black. They swim rapidly 

 and evenly by means of rapid rowings with their legs, 

 which are thickly fringed with long hairs. I have one 

 here, which seems to be the Hydrachna histrionica. It is 

 a little, flat, circular, cushion- or cake-like creature, scar- 

 let, with four clouds of black on its back, about one-sixth 

 of an inch in diameter. You may notice the effective oars 

 which the legs form by means of their thick fringe of hair, 

 and in particular the power which the hind pair possess 

 by reason of the enormously dilated hip -joint, affording 

 space for broad and powerful muscles. 



The structure of the mouth differs greatly from the 

 same parts in the Cheese-mite. The palpi here are long 

 and perfectly free throughout; the fourth joint is long 

 and slender, and is curiously hollowed at the end to re- 

 ceive the terminal joint, which forms a short claw, and 

 which falls down upon the former. The mandibles, too, 

 are not pincers, but consist each of a thick joint cut off 

 obliquely behind, like the nib of a pen, while the other 

 extremity is blunt and broad, and bears a strong curved 

 claw; the lip is oval, and cleft in the middle, and is 

 wedged in between the bases of the first pair of legs. 



