WATER-MITES AND THE WATER-BEAR. 289 



also the two posterior. Occasionally the anterior 

 groups on opposite sides are in contact at the median 

 line, as in Fig. 195. The ventral plates are oval, their 

 greatest length generally being from before backward, 

 and usually close together. The two oval, lateral 

 pFates are oval from side to side, and sometimes 

 curved. The mouth is small, round, and encircled by 

 a ring-like hood. The skin is usually hard and rough- 

 ened, or covered by a deep network of strongly elevated 

 lines, which give it a beautiful appearance. The skin 

 is sometimes shed in captivity, and is not rarely found 

 as a torn, emptj', and colorless net, quite worth ex- 

 amining with a high power. There are some soft- 

 bodied species but they do not seem to be common. 



The body of both the male and female is truncated at 

 the posterior border, but the male has a peculiar short 

 prolongation projecting from the center of that mar- 

 gin, as in Fig. 196, the shape of the part varying 

 greatly in the different species. The females are the 

 most numerous and those most frequently met. 



The upper surface or back of both sexes often bears 

 a deep, depressed line, sometimes enclosing a small 

 circular or oval area confined to the posterior extrem- 

 ity, sometimes a large space, including the greater 

 part of the entire back. From others it may be 

 absent. 



The eyes are two, black, and separated. The color 

 of the body is very different in the numerous species. 

 It may be blue, green, yellow, red, or almost any 

 bright tint, either diffused or confined to distinct parts. 

 Thus in one female Arrenurus the center of the body 

 is brown, the sides blue, and the coxae yellow. In an- 

 other the body is red, the cceca vermillion. Another, 



