BRACHIONUS. 49 



3. The mouth is at the ventral border of the trochal disk and 

 leads by. a short buccal cavity to the mastax, which is a muscu- 

 lar apparatus provided with three chitinous trophi (a median 

 incus and two viallei). It is used in grinding the food. The 

 grinding movements are easily seen. A very short gullet leads 

 from the mastax to the large stomach. The intestine is short 

 and thick and opens into a cloaca. The anus is near the base 

 of the tail, on the dorsal surface. 



4. The reproductive and excretory systems are not easily 

 seen. An ovary and a large vitellarium are present. The ovi- 

 duct opens into the cloaca. Two long nephridial tubes open into 

 a contractile vesicle that in turn opens into the cloaca. 



5. There is a single ganglion in the anterior dorsal region, 

 immediately beneath two red eye-spots. Anterior to the eye- 

 spots is a dorsal feeler, which is a tactile organ. 



There are many common rotifers that have no lorica and 

 some of them have the trochal disk two-lobed. 



