EOTATORIA. 651 



or points. The circular arrangement of the cilia forms what are 

 called the wheels. By the successive vibration of these, the ap- 

 pearance of a continual rotation is produced ; and their action 

 creates rapid currents in the surrounding fluid, by which the 

 supply of food is obtained, consisting of other animalcules of 

 still smaller size, and less complex structure. Between the 

 wheels, the head is occasionally protruded, bearing two red spots, 

 supposed to be eyes; on its under surface there is a projecting 

 tubular spike, which is believed to act as a syphon conveying 

 water into the general cavity to aid perspiration. The vital 

 power of some specie? Is extraordinarily great, they having been 

 known to revive after being kept in dry sand for four years. 

 The wheel-animalcules do not propagate by spontaneous division, 

 but by eggs inconceivably minute, so that they can be raised in 

 the air with vapor, and transported in every direction. Much 

 diversity of opinion has existed in relation to the proper classifi- 

 cation of these animalcules, of the wonderful structure and variety 

 which the microscope has made such interesting revelations ; but 

 the lengthened form of their bodies, the location of the mouth and 

 eyes at. one extremity ; the occasional appearance of cross or 

 transverse lines shadowing forth a division into segments ; and 

 especially the character of the nervous system, so far as it can 

 be ascertained, are among the proofs that they should have a place 

 with the Articulates. With these, Dr. Grant was one of the first 

 to place them. Leydig proposed to call them CILIATED CRUSTA- 

 CEANS. We follow the suggestion of Prof. Dana in placing them 

 next the Cirripedes. 



The common species, Rotifa vulgarls, is remarkable for the 

 two circles of vibratile cilia or vibrillse, referred to above, and 

 for the posterior forceps or pincers. One species (Melicerta 

 ringens) has the power to withdraw itself into an outward case; 

 and has the vibratile cilia distributed into four divisions. 



