402 ROTLFERA. 



concerned in locomotion, but in addition they play an important part 

 in attracting small particles of food. There is also a second row of 

 delicate vibratile cilia, extending on either side from the dorsal edge 

 of the trochal disc to the mouth [parts of the continuous border of 

 cilia just mentioned as starting from the mouth], which is placed on 

 the ventral side of the trochal disc. These cilia serve to guide the 

 small food particles which are captured by the trochal disc into the 

 mouth. 



Alimentary canal. The mouth leads into a dilated pharynx (fig. 

 324), provided with a special armature. The parts of the armature 

 are in continual movement, and serve for mastication. Following 

 the pharynx there is a short cesophageal tube ; this leads into the 

 digestive sac, which is lined with large ciliated cells. The anterior or 

 gastric part of this cavity is wide, and receives two large glandular 

 tubes, which may sometimes be resolved into unicellular glands. 

 They may be explained from their function as salivary or pancreatic 

 glands. The posterior narrow intestinal part usually opens into a 

 cloaca] chamber, which is likewise ciliated and opens on the dorsal 

 surface at the point where the foot4ike posterior region joins the 

 anterior part of the body. In some Rotifer a, as for example Asco- 

 morpha, Asplanchna, the intestine ends blindly. 



A blood-vascular system is always wanting, and the body cavity 

 is filled with a clear vascular nuid. The structures, erroneously 

 described by Ehreiiberg as vessels, are in reality the transversely 

 striped muscles and muscular networks beneath the integument. 



Respiration is carried on by the general surface of the body; 

 special organs of respiration are wanting. 



Excretory organs. The so-called respiratory canals are excreto'ry, 

 and correspond to segmental organs. They consist of two sinuous 

 longitudinal canals with cellular walls and with nuid contents, and 

 they communicate with the body cavity by ciliated funnel-shaped 

 openings placed at the end of short ciliated lateral branches (vibratile 

 organs). They open into the cloaca either directly or by means of a 

 contractile vesicle (respiratory vesicle). 



The nervous system is allied to that of the Platyhelminthes. The 

 central part of it consists of a simple or bi-lobed cerebral ganglion 

 placed above the oesophagus, and giving off nerves to peculiar cuta- 

 neous sense organs and to the muscles. Eyes are often present, and 

 lie upon the brain either as an x-shaped unpaired pigment body or as 

 paired pigment spots provided with refractile spheres. The above- 

 mentioned cutaneous sense organs, which are probably tactile, h;ive 



