216 



LIFE, IN ITS INTERMEDIATE FORMS. 



imbedded in the flesh, like the roots of a tree in the soil, 

 resist all opposing influences to drag it away. This form 

 is one of the most bizarre of the whole ; for, besides this 

 strange rooting head which is concealed, the exposed body 

 resembles a twisted sausage, without limbs, to which the 

 external ovaries hang, like rolls of thread twined loosely 

 together. 



Every ditch and pool is tenanted by tiny nimble crea- 

 tures, which move through the water by a succession of 

 little leaps, whence they are called Water-fleas. Some- 

 times the ponds swarm with them to such a degree that 

 the fluid contents seem not water but blood, or other 

 strange liquid, according to the colour of the little animals. 

 These belong to the Order Entomostraca, and, though 

 small, many of them being undistinguishable without 

 microscopic aid, they are highly curious. Many of them 

 are enclosed, either wholly or in great measure, in a shell, 

 which takes the form of two convex plates, either soldered 

 together down the back, or united there by a hinge, leav- 

 ing the opposite edge free for the protrusion of the head 

 and feet. The close resemblance of the latter (Cyprididce) 

 to the bivalve shells of Mollusca is remarkable. 



In general these little animals have but a single eye in 

 the middle of the forehead, which is of large size in pro- 

 portion, round, and generally of a brilliant red hue, glis- 

 tening like a ruby, so that it furnishes a beautiful study 

 under the microscope. In the common Water-flea (Daph- 

 nia pulex), the eye is bluish black, evidently composed of 

 about twenty crystalline lenses, and though quite in- 

 cluded within the shell, its motions, which are quick and 

 partly rotatory, can be distinctly perceived. 



