214 AQUATIC MICROSCOPY FOR BEGINNERS. 



Most of these animals have eyes at some period of 

 their life, or little red or black specks supposed to be 

 imperfect eyes. They are often to be noticed near 

 the front of the body in young individuals, but in the 

 old they are as often absent. Their number and posi- 

 tion have sometimes been used as characters by which 

 the genera and species were classified, but, since they 

 often disappear with age, they can be of little value 

 for this purpose, certainly of none to the beginner. 



The eyes, when present, are almost without excep- 

 tion, attached to the brain, which in some Rotifera, is 

 an enormous organ,, often filling most of the front re- 

 gion in advance of the eye. Such Rotifers should be 

 among the most intelligent of animals, if intelligence 

 is ever commensurate with mere mass and not with 

 quality, and fineness of structure. 



The body is inclined to be cylindrical, yet there are 

 some that resemble flat disks and oblong figures. 

 Neither are they all free-swimming. Some are per- 

 manently adherent to the leaflets of aquatic plants or 

 to other submerged objects, but these generally form 

 a protective sheath about themselves, into which they 

 retire when frightened or disturbed, in a manner simi- 

 lar to that of some Infusoria; and, as in the Infusorial 

 loricee, the sheaths may be formed of a stiff membrane 

 or of the softest and most gelatinous material, or they 

 may be built of particles of flocculent rubbish, or of 

 rejected food-fragments. In all instances the sheaths 

 are the work of the Rotifers inhabiting them, and 

 none of the sheath-building Rotifers are free-swim- 

 mers.* Most of the free-swimmers, however, may 



*Since the foregoing was written three have been discovered in 

 England. But this need not trouble the beginner. 



