THE ROTIFERA. 57 



tures near the neck, (see pi. xn, fig. 3, c); and in some 

 kinds there are internal oval bodies, composed of gran- 

 ules, or corpuscles, which have constantly a tremulous 

 motion, and are supposed to perform the office of bran- 

 chia, or gills. 



There are indications of nervous centres, or ganglia, 

 in several genera ; and from one to four punctiform eyes 

 have been observed in 150 species: in some there ap- 

 pears to be a ganglion, or nervous mass, immediately 

 beneath the eye. Some kinds are oviparous, others 

 viviparous. An elongated bag or sac, in which the 

 ova, or eggs, are formed, is distinctly visible; but few 

 eggs are developed at the same time. The ova, in many 

 species, equal in size one-third of the body of the ani- 

 malcule. They retain their vitality for almost an un- 

 limited period, and are transported by the water, and 

 wafted by the winds for, whether dry or moist, they 

 remain uninjured till, thrown into the conditions suit- 

 able to their organisation, they become developed, and 

 the apparently pure waters suddenly teem with myriads 

 of highly organised beings. Even the adult animals of 

 some species the common Rotifers, for instance after 

 being apparently dried up for several years, will start 

 into life upon the addition of a few drops of water, 

 and throw their rotatory organs into full play, as if 

 roused from a refreshing slumber. 



