ENTOMOSTRACA AND PHYLL6pODA. 259 



all formed of short and well-marked joints, the num- 

 ber varying greatly in the different genera, sometimes 

 in different species of the same genus. 



One or more black or dark-red eye^spots are com- 

 monly present. In some the eye is single, and in the 

 center of the forehead. It may also be slightly mov- 

 able at the will of its possessor. The young animal, 

 as not rarely happens, may have two distinct eyes, 

 which, as it grows older, become joined into one and 

 cov^ered by the shell. In many forms there is in addi- 

 tion to the true eye, a collection of opaque matter 

 usually situated behow the eye but which may be mis- 

 taken for it. This is the so-called "pigment fleck," 

 which, in some Entomostraca, is supposed to act to a 

 certain degree as an eye; It is" never movable, as the 

 true eye often is, and by this immobility may be 

 recognized. A careful examination of the true eye 

 with a comparatively high-power objective, will reveal 

 still further differences between it and the pigment 

 fleck. The reader should, however, be on his guard, 

 and not too hastily decide that the specimen has more 

 than a single eye. 



The heart is frequently visible, especially in the 

 shell-bearing forms, being there placed at the back of 

 the body near the head. It beats. rapidly, and appar- 

 ently sends the colorless blood quickly through the 

 system. 



All these animals increase and multiply through the 

 formation of eggs, which may remain within the shell 

 and there be hatched, or they may be attached to the 

 parent's body in external clusters. In the shell-bear- 

 ing forms they are passed into a brood cavity 

 at the back between the body and the shell, where 



