GENERAL ZOOLOGY 



Flame , 



External opening 



Flagellum 



Lumen 



Flame cell 



Nephridiostome 



Septum 



Lumen 



Fig. 17.6. Some excretory mechanisms in in- 

 vertebrates. A, protonephridia! system of 

 Pedtcellina, an entoproct (pp. 356-357). B, 

 portion of a solenocytic protonephridial unit of 

 the polychaete annelid Phyllodoce, shown in sec- 

 tion. C, nephridiostome of a nephridium in 

 another polychaete, Trypanosyllis; note the ar- 

 rangement of cilia in the open funnel and prox- 

 imal parts of the tubule (cf. nephridium of 

 Lumbncus, Fig. 14.9, p. 408). (.4, from C. Cori 

 in W. KiJkenthal and T. Krumbach, 1933, Hand- 

 buck der ^oologie; B and C, from C. G. Rogers, 

 Textbook of Comparative Physiology, copyright 

 1938 by McGraw-Hill Book Co., Inc., reprinted 

 by permission.) 



Septum 



much reduced. In an apparently entirely different environmental situation, 

 but one governed by the same need to conserve water as that facing marine 

 animals, some species of earthworms adapted to dry terrestrial conditions 

 have been found with nephridial systems unlike those of the common forms. 

 In these specialized annelids, the nephridia open not on the surface of the 

 body but into the digestive tract, where active reabsorption of water occurs 

 through the intestinal wall into the blood. 



Malpighian tubules, developed in most terrestrial arthropods, apparently 

 represent an analogous adaptation for water conservation. Nitrogenous 



520 



