452 THE MICROSCOPE. 



thickened and rendered opaque by the addition of the 

 dark material, which I conjecture to be the fsecal pellets 

 sucessively discharged in process of growth. Contrary to 

 the rule in the allied genera, the petal oid disc is made to 

 open by the bending forward of the head towards the 

 Tentral aspect, and its widest margin is the dorsal one. 

 Immediately behind the disc are two minute lateral horn- 

 like points, which project from the head, and curve to- 

 wards each other. These are sometimes visible both in a 

 frontal and a lateral view, and with the disc closed or 

 open ; but at other times the closest scrutiny fails in dis- 

 cerning them. Behind these, in the median line, there 

 is an organ which is never concealed : it is the single 

 antenna, which stands up perpendicularly from the occiput 

 to a great height (being almost half as long as the body, 

 exclusive of the foot), and generally arches over the front, 

 but is capable of vigorous and sudden movements to and 

 fro, and from side to side. It is evident!}^ tubular through- 

 out ; either a simple tube with thick \Yalls, or else, if the 

 walls are thin, furnished with a slender piston which runs 

 through its length. 



" The Cephalosiplion is very lively and active in its 

 motions. It is very ready to protrude from its case, and 

 not at all prone to retire upon ordinary alarms, such as a 

 jar upon the instrument, that woukl send the Floscidaria 

 or the Stephanoceros into its retreat in an instant. It is 

 very curious to see it protruding : the long antenna is first 

 thrusl out, and jerked to and fro as a feeler, exploring the 

 surrounding water for safety. The entire height of an 

 average specimen, in its ordinary state of extension, is 

 l-33d of an inch ; of which the foot is l-50th, the body 

 l-200th, and the antennas l-400th of an inch. 



The rotating or wheel-animalcules occupy the most 

 conspicuous place among infusorial animals. They re- 

 quire water for their development, although tliey are 

 indwellers occasionally of the cells of mosses and damp 

 weeds. They do not possess mcniy stomachs, but one, 

 and genertdly have teeth and jaws to supply its wants. 

 They can elongate and contract their bodies, and FCme 

 species have their extremity prolonged to a tail, or rather 

 a foot, or a forked process, by means of which they 



