VIlJ 



ANATOMY 



123 



17 



14 



19 



The excretory system consists of two longitudinal ducts con- 

 sisting of columns of perforated cells, which bear a number of small 

 tags hanging freely into the body-cavity (Fig. 52), i.e. of two long 

 nephridia beset with short branches terminating in solenocytes 

 each containing a cavity in 

 which a bundle of flagella wave 

 slowly about. In Floscularia 

 four or five pairs of solenocytes 

 have been seen. The longi- 

 tudinal ducts are usually con- 

 nected by a transverse duct just 

 under the disc, and they open 

 as a rule into a capacious bladder 

 which contracts at intervals and 

 expels its contents into the cloaca 

 and thus out of the body. It has 

 been calculated that in some 

 species this bladder expels a bulk 

 of fluid equal to that of the 

 animal about every ten minutes, 

 and this fluid must be replaced 

 by water which diffuses through 

 the body- wall. This water doubt- 

 less brings with it oxygen and 

 carries off carbonic acid which 

 it has taken up from the tissues. 



The principal part of the 

 nervous system is a bilobed 

 ganglion called the brain. This 

 lies just under the disc on the 

 dorsal side of the mastax; it 

 bears two red eyes in Floscu- 

 laria. In Notommata the brain 

 is large, and on it more than 

 one pair of eyes are situated. 

 In the Bdelloida there is also a 

 ganglion on the ventral side of 

 the mastax, and a pair of cir- 

 cumoesophageal cords unite .this with the brain, in Floscularia, 

 as in Rotifera generally, there are three well-marked sense organs 

 called antennae, consisting of prominences bearing stiff sense hairs; 



12 



FIG. 52. Diagram of a Kotifer. 



I. Anus. 2. Brain. 3. Trochus. 

 4. Cingulum. 5. Gland in foot. 

 6. Cloaca. 7. Cuticle. 8. Ecto- 

 derm. 9. Dorsal antenua. 10. Eye. 

 .11. A ciliated "tag" of the excre- 

 tory system. 12. Intestine. 

 13. Muscles. 14. Mouth. 15. Ne- 

 phridial tube. 16. Ovum. 17. Ovi- 

 duct. 18. Ovary. 19. Mastax. 

 20. Stomach. 21. Bladder. 

 22. Vitellarium. 



