320 



ZOOLOGY 



SECT. 



the cloaca from the proctodseurn. Between the body-wall and the 

 enteric canal is a spacious body-cavity containing a fluid which 

 serves the purpose of blood and contains minute granules. 



The excretory system consists of paired nephridial tubes 

 (Figs. 269 and 272, nph.) resembling those of the Platyhelminthes. 

 Their general direction is longitudinal, but they are a good deal 

 coiled and give off little tag-like processes ending in flame-cells. 

 Upon the end of each tag, projecting into the body-cavity, is a long 

 flagellum. The lumen of the tubes is intra-cellular : it is uncertain 

 whether or not the cavities of the flame-cells communicate with the 

 body-cavity by apertures in their walls. Posteriorly the nephridial 

 tubes open into a bladder or contractile vesicle (c. v.), the contents 

 of which are discharged, by periodical contractions, into the 

 cloaca. 



FIG. 272. Diagram of a Rotifer, a. anus ; br. brain ; c 1 . pre-oral, and c 2 . post-oral circlet of 

 cilia ; r. gl. cement gland ; cl. cloaca ; CM. cuticle ; c. v. contractile vesicle ; d. ep. deric 

 epithelium ; d.f. dorsal feeler ; e. eye ; fl. c. flame-cells ; int. intestine ; m. muscles ; mth.* 

 mouth; nph. nephridial tube ; ov. ovum ; ovd. oviduct ; ovy. germarium ; ph. pharynx; 

 st. stomach ; vt. vitellarium. 



Nervous System and Sense Organs. There is a single 

 ganglion or brain (Figs. 269 and 272, br.), of proportionally large 

 size, situated at the anterior end of the body, above (dorsal to) the 

 mouth and pharynx. On the dorsal surface of the brain, where it 

 comes into contact with the body- wall, is a small red eye-spot (e.). 

 The only other organs which can be considered as sensory are 

 three structures known as tactile rods or feelers ; one of these (d. f.) 

 is a small cylindrical process tipped with stifi hair-like bodies, 

 which projects from the dorsal surface just behind the trochal disc : 

 the other two (I. /.) are paired, situated on the dorsal surface of 

 the lorica and not prominent. 



The tail contains a pair of cement glands (c. gl.), by the secretion 

 of which the animal is able temporarily to attach itself. 



Reproduction and Development. The sexes are lodged 

 in distinct individuals, which present a striking degree of sexual 



