Spoon-worms and Leeches. 



FIG. 39. 



but which remain permanently in this ciliated condi- 



tion. In these, the ciliary lobes are prominent and 



rounded, acting as locomotory organs, and from the 



rapid vibration of the cilia which clothe them they 



seem like rotating wheels, hence these 



little creatures are called Rotatoria. They 



are microscopic in size varying from 3-^o tn 



to Jth of an inch in length, but from the 



exquisite transparency of their bodies the 



details of their organisation can be seen 



by the aid of the microscope. The male 



rotifers are few and small and have no 



digestive canal ; the females have a com- 



plex nutritive system, and many species 



are provided with an organ of mastication 



like an anvil acted on by two hammers. 



These animals can bear much ill usage, 



and are capable of reviving again on being 



moistened, after having been almost com- 



pletely dried up. 



On irritation the trochal disks (fig. 

 39, c] can be retracted into the cavity of 

 the body, from which they are gradually 

 protruded again on the cessation of the 

 stimulus. Some rotifers are rooted ; 

 others possess a forceps posteriorly, 

 whereby they can hold on to foreign 

 bodies ; others again are contained in 

 sheath, into which they 

 being irritated. 



CLASS VI. Spoon- worms or Squirt- worms, 

 Gephyrea. These are interesting marine worms whose 



F 2 



a vase-like 

 can retract themselves, on 



