.MUSEUM OF COMPARATIVE ZOOLOGY. 26 



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which clearly supports the view that Amphioxus is closely related to 

 Craniotes and occupies a position near the base of the Vertebrate phylum, 

 the kidneys of this animal are of prime interest in the present connection. 

 Notwithstanding the extreme importance of the subject, however, the 

 relation of the excretory system of Amphioxus to other Chordates must 

 still be regarded as a matter of considerable doubt. 



At least seven different views have been advanced respecting the excre- 

 tory organs of this animal. According to the earliest of these views, 

 which originated with Joh. Muller ('42, p. 101, see also Langerhans, '76, 

 p. 322, and Rolph, 70, p. 140), certain modified groups of cells lying in 

 the posterior portion of the atrium are claimed to possess an excretory 

 function. I presume that no morphologist would endeavor to homol- 

 ogize these excretory patches with the kidneys of A^ertebrates. The 

 same is true of the glandular structures described by Owen ('66, p. 533, 

 Fig. 1G9, k), and the epithelial bands of Wilh. Muller ('75, p. 109). 

 Nor- can I see in the "pigmented canals," atrio-ccelomic funnels, of 

 Lankester ('75, pp. 260, 261, and '89, pp. 394-397) any features which 

 would definitely link them to Vertebrate nephridia. 



The account given by Hatschek ('84) of his discovery of a single 

 nephridium, which he believes to open into the pharyngeal cavity, is too 

 brief to permit one to form a final judgment upon his interpretation. 

 The observation has not been confirmed by any subsequent investigator 

 save perhaps Lankester and Willey ('90, p. 459), who do not however 

 regard this organ, which they call the sub-chordal tube, as a nephridium. 

 There is nothing in its structure as described by either author which in 

 my opinion justifies its comparison to a Vertebrate excreton r tubule. 



The most recent paper on this topic, which is by Weiss ('90), is of 

 considerable interest from the physiological researches which it records : 

 these show that a large portion of the atrial epithelium, as well as the 

 excretory patches of Muller, have a well marked excretory function. Of 

 greater morphological value is the description given by Weiss of certain 

 small tubules in which the excretory function is peculiarly active. These 

 tubules empty into the atrium at the upper margin of that cavity in the 

 region of each secondary gill bar. They seem to project into the ccelom, 

 but Weiss was unable to detect a continuity between their lumen and 

 the ccelom. Since the relations of these tubules to the ccelom are not 

 ascertained, I am of opinion that the observations of Weiss do not afford 

 satisfactoiy reasons for regarding them as homologues of either the Ver- 

 tebrate or the Annelidan nephridia. Weiss's account, however, is at 

 least very suggestive. An important feature is the metamerism of the 



