318 



ZOOLOGY 



SECT. 



opposite or dorsal surface is convex both from before backwards, 

 and from side to side. 



The anterior portion of the body projects from the lorica in the 

 form of a transverse disc (tr. d) with a prominent edge fringed with 

 cilia : this is the trochal disc, and is one of the most characteristic 

 organs of the class. By the action of the cilia the animal is 

 propelled through the water, and, as in Vorticella, their successive 

 flexion gives an appearance of rotation to the disc or " wheel- 

 organ " whence the name of the class is derived. Within the circlet 



FIG. 269. Brachionus rubens, female. A, from the dorsal aspect ; B, from the right side, 

 a. anus ; br. brain ; d. f. dorsal feeler ; c. gl. cement-gland ; cl. cloaca ; c. /. ciliary lobes ; 

 c. v. contractile vesicle ; e. eye-spot ; int. intestine ; Ir. lorica ; 4. f. lateral feeler ; m. : 

 muscular bands ; nph. nephridial tubes ; ov. germarium : ph. pharynx ; st. stomach 

 t. tail ; tr. d. trochal disc ; vt. vitellarium. (After Hudson and Gosse.) 



of cilia arise three prominences (c.l.) covered with cilia of large 

 size. The trochal disc is not perfectly symmetrical, but has at one 

 part of its circumference a depression in which the mouth lies : 

 this marks the ventral surface. The anus (a.) is dorsal in position, 

 and is placed at the junction of the tail with the trunk. 



The body-wall consists of an epidermal layer, without cell- 

 limits, covered by a chitinoid cuticle : it is by a thickening of the 

 latter in the region of the trunk that the lorica is produced. 



