126 SYSTEMATIC ZOOLOGY 



oesophagus, joining on the ventral side a large ganglionic mass 

 in the trunk region. The Chaetognatha are hermaphroditic ; 

 the ovaries, or female germ-glands, lie in the trunk segment, and 

 the oviducts open near the anus. The testes, or male germ- 

 glands, are found in the tail segment. 



SUBTYPE V. ROTIFERA 



The Rotifera (Lat. rota, a wheel, and ferre, to bear) or 

 Rotatoria (Lat. rotator, whirler), the " wheel animalcules," are 

 microscopic animals, living for the most part in fresh water or 

 in moist places, though some are marine. They may be found 

 in almost any pool of stagnant water. A few are parasitic, but the 

 greater number are free-living. Most of them are free-swimming, 

 but some are attached, and secrete a sort of tube around them- 

 selves for protection. We can distinguish three regions to the 

 body, a head, a trunk, and a tail, but the tail is often greatly re- 

 duced. The head region is always provided with numerous cilia 

 very variously arranged in the different groups, and these assist in 

 locomotion and in bringing food to the animal by means of the cur- 

 rents which they set up in the water. On the ventral side of the 

 head is the mouth. The trunk generally possesses a thickened 

 cuticula, which forms a sort of shell ; this is called the lorica, and 

 is often provided with spines and ridges, and sometimes exhibits 

 rings suggesting segmentation. The tail is more or less retractile. 

 and is generally provided with a pair of pincer-like appendages 

 at the posterior end for attachment ( Fig. 117). 



The mouth leads into an enlargement called the pharynx, which 

 is provided with a fairly complicated set of chitinous plates form- 

 ing the masticatoiw apparatus. This is succeeded by the stomach, 

 the intestine, and the anus, which opens at the posterior end of 

 the trunk on the dorsal side. There is a large body-cavity, which 

 contains, in addition to the alimentary canal, the single germ- 

 gland, whose duct opens into the posterior end of the intestine. 

 At about the same point is the opening of the excretory tubules, 

 of which there are two, one on each side of the both - , more or less 

 convoluted and slightly branched. The nervous system consists 

 ol a brain, lying dorsal to the pharynx, and bearing on the dorsal 

 surface a single pigment spot, the eve. 



The sexes are separate, and the males are generally much more 





