320 STRUCTURE OF WHEEL-ANIMALCULE. 



prolonged into a tail, possessing three joints, each of which has a 

 pair of prongs or points. These joints can be drawn up within 

 each other, like the sliding-tubes of a telescope. Within the ex- 

 ternal integument there are four longitudinal bands running 

 from end to end ; these are probably bundles of muscular fibre, 

 by the contraction of which the body may be shortened. The 

 cilia are disposed in two circles, forming what are termed the 

 wheels. By the successive vibration of these, the appearance of 

 a continual rotation is produced ; and their action creates rapid 

 currents in the surrounding fluid, by which the supply of food is 

 obtained. A sort of whirlpool is created by each .wheel, which 

 brings towards the mouth the minute animalcules and other 

 particles floating in the neighbourhood ; and those which are not 

 swallowed, are carried off by a return-current. Between the 

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

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

 projecting spike (c), which is observed to be tubular, and which 

 is believed to act as a siphon for the introduction of water into 

 the general cavity, for the purpose of respiration. The oeso- 

 phagus terminates in a sort of gizzard, provided with regular 

 teeth at its entrance (d). These teeth are two in number on 

 each side, and are fixed upon hard jaws, moved by powerful 

 muscles, so as to work between each other. All the food which 

 is swallowed is submitted to their action, before it enters the 

 first stomach ; and when the cilia are in operation, these jaws 

 are always in regular movement. From the first stomach there 

 passes off in the Rotifer a long straight intestine (/,/)> whidk 

 terminates without any dilatation except near its close (#), just 

 at the commencement of the tail. But in many other Rotifera 

 we find the gizzard opening into a larger cavity, which may be 

 regarded as the true digestive stomach. Near the termination 

 of the intestine is the opening of the passages, by which are ex- 

 truded the eggs (k), that are formed in the large ovaria. These 

 eggs often attain so great a degree of development, while yet 

 within the body of the parent, that the ciliary movements of the 

 embryo may be seen ; and the young may be said to be born 

 alive, being capable of active locomotion, and of obtaining their 



