WATER-MITES AND THE WATER-BEAR. 287 



The young resemble the parent, it is said, in all except 

 size. 



This strange bear-like creature is not rarely to be 

 found at the bottom of shallow ponds; or, if an 

 aquarium is kept, it will be almost sure to make the 

 bottom its home. It is entirely invisible to the naked 

 eye, measuring rather less than one-sixtieth of an inch 

 in length. On account of their slow movements, the 

 water bears are often called Tardigrades. The scien- 

 tific name of the common American form is Macrobid- 

 tus Americd)ius. 



2. Diplod6ntus. 



This mite may be recognized by the form of the 

 ventral plate as given in the Key, and by the fact that 

 the plate is roughened by minute granules. The eyes 

 in one species are two in number, very small and wide 

 apart. They are placed on the edge of the front bor- 

 der. In another species they are four, and are placed 

 so far forward on the front margin that they are best 

 seen when the animal is on its back, and thus exam- 

 ined from beneath. The coxae are in four separate 

 groups. The body of the two-eyed species has the 

 front part black, spotted with red, and the posterior 

 region red, with a central longitudinal black band. 

 The one with four eyes has the entire body bright red. 



3. HydrAchna (Fig. 193). 



The anterior coxae on the same side form a single 

 group, being in contact by their whole Ifength; the 

 middle coxa is entirely disconnected from the others; 

 the most posterior is the largest, and is also entirely 

 distinct. 'In one species the body is spherical and 



