CRABS AND SHRIMPS 207 



when the curious receptacles, being no longer needed, are 

 thrown off, and speedily decay. 



Here is a second form. It is named Lynceus, and is 

 nearly as common as the Cyclops in our stagnant pools. 

 Essentially its structure is the same, but it has this pecu- 

 liarity, that its body is enclosed within a transparent shell, 

 which is thin and flattened sidewise, and through whose 

 walls all the movements and functions of its parts are dis- 

 tinctly visible. The shell is broadly ovate in outline, 

 comes to a sharp edge above, but is open all along the 

 lower half of its circumference as if two watch-glasses 

 had been soldered together, edge to edge, and then a por- 

 tion of the semicircumference had been ground away, so 

 as to leave a thin but long entrance. Through this narrow 

 orifice the limbs are protruded for locomotion, and through 

 it the surrounding water finds its way in currents, bringing 

 oxygen to be respired and food to be devoured. 



The translucent shell descends in front into a sharp 

 long beak, below which are seen the organs of the mouth, 

 .two pairs of foot- jaws, beset with fine bristles. At the 

 origin of the beak is the eye, consisting, as we saw in the 

 Cyclops, of several lenses, enveloped in a common cornea, 

 the whole forming a movable organ of a blue-black hue. 

 Just behind this, at the very highest part of the shell, is 

 a little colorless bladder-like vesicle, which constantly 

 maintains a rapidly alternate contraction and dilatation. 

 This is the heart, and this motion circulates the blood. 



Below this, there is seen a great translucent irregular 

 mass of flesh, evidently comprising many viscera, which 

 winds along from one end of the shell to the other, nearly 

 occupying its entire area, but not in connection with it at 

 the hinder part, as we see by its free movements there, 



