506 



ZOOLOGY 



SECT. 



S.CIefDsine 



Another interesting condition occurs in Nephelis, in 

 which the middle region of the body contains a series 

 of paired, metamerically arranged spaces, surrounded 

 by botryoidal tissue and containing the nephrostomes. 

 Development shows that these cavities are derived 



from true ccelomic 

 spaces in the embryo, 

 formed, as in Chaeto- 

 poda, by a splitting 

 of the mesoderm in 

 ^ r each segment. Acan- 

 thobdella, already re- 

 ferred to as excep- 

 tional in the posses- 

 sion of setae, is also 

 the only member of 

 the class which has 

 a well-developed and 

 spacious ccelome, 

 divided by mesen- 



3.BrcmcTh7llion teries into !>umber 

 of segments. 



1. Ron hob del la In most instances 



FIG. 420. Three Rhynchobdellida. br. gills ; pr. everted the skin, with its 

 )oscis. (1, after Bourne ; 2 and 3, after Cuvier.) abundant Supply of 



capillaries, constitutes the only respiratory organ, but in 

 BrancMlion (Fig. 420, 3), a Rhynchobdellid para- 

 sitic on the Electric Rays (Torpedo and Hypnos), 

 and on one of the Australasian Skates (Raja 

 nasutd), differentiated respiratory organs or gills 

 (br.) are present in the form of delicate lateral 

 outgrowths of the 

 segments. 



In most members 

 of the class the neph- 

 ridia are formed on 

 the same general type 

 as those of Hirudo, 

 but differ in the struc- 

 ture of the ciliated 

 funnels, which may 

 be more or less modi- 

 fied, as in Hirudo. 

 The funnels, where 

 they occur, never open 



into the nephridial FIG. 421. Proboscis of Clepsine. A, retracted ; B, eveite d ; 

 panalc TTank {urinal cr - cr P > ff ut ' gullet; mth. mouth; pr, introveit ; s. gl. 

 Canals. J^acJl tunnel salivary glands. (After Bourne.) 



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