THE ROTIFERA. 57 



tures near the neck^, {see pi. xii, 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. 



