316 BULLETIN OF THE 



dence in support of an intimate relation between Vertebrates and Plat- 

 helminthes is afforded by a comparison of their excretory organs. 



In Nemertines the excretory system is in peculiar relations with the 

 blood vascular system. According to Oudemans ('85). the excretory 

 system of the Schizonemertini and the Hoplomertini consists of a longi- 

 tudinal tube, which is closely applied to the lateral longitudinal blood- 

 vessel of the oesophageal region, and this tube communicates with the 

 exterior by means of a single excretory pore or by a number of such 

 openings. In Carinella and Carinoma, however, the connection is much 

 more intimate, and the glandular portion of the excretory organ lies 

 embedded in the oesophageal blood lacuna? and communicates with the 

 latter by means of two or three evident openings. Oudemans asserts, 

 indeed, that the excretory system is in reality a detached portion of the 

 blood vascular system. Burger ('90, p. 92), however, has recently 

 thrown some doubt upon the existence of open communications between 

 the nephridia and the blood-vessels, but reaffirms the close dependence 

 of the excretory system upon the vascular trunks. 



Comparing the nephridia of Nemertines with those of Vertebrates, it 

 seems to me that one cannot fail to recognize a pronounced difference in 

 type. In Vertebrates the nephridia are canals in close relation with the 

 ccelom ; they develop from its epithelium, and even in the adult arise 

 from chambers which must be regarded as detached portions of the 

 ccelom. The excretory organs of Nemertines lie between the vascular 

 trunks and the exterior, and show no such relations with the ccelom. 



Among the Annelids, on the other hand, the Chsetopods possess an 

 excretory system, which seems to present several features of strong 

 resemblance with the nephridia of Vertebrates, and it remains to be 

 considered whether an actual homology can be postulated in this case. 



The points of similarity may for the present purpose be classed under 

 seven heads. (1.) The Vertebrate and the Chaetopod excretory systems 

 agree in the fact that both primitively serve, at least in part, to convey to 

 the exterior such fluids as accumulate in the ccelom, this cavity being used 

 as a capacious excretory reservoir. (2.) In both groups certain portions 

 of the epithelial lining of the coelom become differentiated into specialized 

 excretory glands. In Vertebrates the only structures of this character are 

 the glomi and glomeruli ; but in Annelids there is evidence that con- 

 siderable areas of the peritoneum may become modified in this way. It 

 was suggested by Claparede ('69, p. 615), that the chloragogen cells 

 secrete certain elements from the blood and transfer them to the peri- 

 visceral fluid. This view of the function of the chloragogen cells has 



