WHEEL-BEAREBS. 239 



subject of our evening's study. It is inclosed in a glassy 

 shell (lorica) of a long oval form, from which rises on the 

 front half of the back a thin ridge, which in the middle 

 has a height nearly equal to half the diameter of the body, 

 but tapers off at each end. Its base is corrugated with 

 wrinkles. This is not set on symmetrically, but leans over 

 considerably to the right side. Its basal portion is hollow, 

 and is continuous with the general cavity of the shell, for 

 we sometimes see portions of the viscera in its interior. 



The head of the animal is rounded, and divided into 

 several blunt eminences or lobes, which are set with cilia ; 

 these rotate constantly, but irregularly and feebly, and do 

 not make manifest wheels, as Brachionus does. A small 

 antenna projects from the back of the head, capable of 

 being erected or inclined. A long brain descends along 

 the base of the ridge, carrying a bright and rather large 

 crimson eye set like a wart on its interior angle. 



Instead of the flexible and contractile foot of Brachionus, 

 the Whiptail has a single horny spine of great slenderness, 

 and exceeding in length the whole body. This spine pro- 

 bably represents not the foot, but one of the toes at the 

 end of the foot. For it is attached to a very short foot, in 

 the midst of two or three bract-like spines, one of which, 

 longer than the rest, and distinctly movable, probably 

 represents the other toe undeveloped. The long spine is 

 set on by a proper joint, a globose bulb being inserted 

 into a socket, which allows it free motion in all directions 

 except backward. The socket itself is contained in a 

 second joint, the basal part of which is inserted at some 



