162 ROTIFERA. PART in. 



have yet been found, their respiration must be cuta- 

 neous. These animalcules have no nerve-centre in the 

 head, but they have one in each segment of the body ; 

 and they are furnished with a suctorial mouth at the 

 end of a retractile proboscis, on each side of which are 

 two tooth-like styles, the rudiments of lateral jaws. The 

 structure of these creatures is microscopic. 



Hotifera. 



Although the Rotifera are microscopic objects, their 

 organization is higher than that of the Annelida in some 

 respects. They are minute animalcules, which appear 

 in vegetable infusions and in sea-water, but by far the 

 greater number are found in fresh-water pools long ex- 

 posed to the air : occasionally they appear in enormous 

 numbers in cisterns which have neither shelter nor cover ; 

 a few can live in moist earth, and sometimes individuals 

 are seen in the large cells of the Sphagnum or Bog-Moss. 



The bodies of the Rotifers have no cilia; they are 

 perfectly transparent, elongated, or vermiform, but not 

 segmented ; they have two coats, both of which in some 

 genera are so soft and flexible that the animal can as- 

 sume a variety of forms; while in others the external 

 coat is a gelatinous horny cylindrical shell or tunic en- 

 closing the whole body except the two extremities, which 

 the animal can protrude or draw in. The soft kind can 

 crawl over solid surfaces by the alternate contraction 

 and extension of their bodies like a worm, and the stift 1 

 Eotifers are capable of doing the same by the contrac- 

 tility of their head and tail. All can swim by means 

 of cilia or lobes at their head. The greater number pos- 

 sess means of attaching themselves to objects by the 

 posterior end of their bodies and of removing to an- 

 other place. 



The wheel-like organs from which the class has its 



