28 



PHYLUM CEPHALOCHORDA. 



vibratile flagellum, arising from the protoplasm around the nucleus at 

 the internal knobbed end and extending along their whole length so as to 

 project into the excretory tube (Fig. 13). They have been termed soleno- 

 cytes from their resemblance to the fibres found on the excretory tubes 

 of some invertebrates (e.g. polychaetous annelids). The tubes them- 

 selves are lined by a ciliated epithelium and a tuft of specially long 

 cilia projects through the renal opening into the atrium. They receive 

 a special vascular supply from the dorsal ends of the pharyngeal vessels, 

 the blood being returned into the adjacent aorta. That these organs are 

 excretory is inferred from their structure, which, as stated, closely resembles 

 that of the excretory organs of some polychaetous annelids, etc., among 

 the invertebrates, and on account of Weiss' experiments. He fed the 



ms 



■m 



VlQ. 12. — Dorsal portion of the left pharyngeal wall of AmpMoxus, showing three renal 

 canals, on one of which the solenocytes are siiown ; seen from the side, diagrammatic (from 

 Korsclielt and Heider after Boveri). Id optical section of the folded ventral wall of the 

 dorso-pharyngeal coelom (ligamentum denticulatum) ; m myotome ; ms intermuscular 

 septum ; nc termination of the branches of the renal tube with the solenocyte? removed ; 

 nk renal canal ; np opening of the renad canal into the atrium ; s synapticulum ; I primary 

 gill-bar ; II tongue bar. 



animal with finely-divided carmine, and then found that the cells of the 

 main tubes contained carmine particles. But he also found carmine in 

 the lining cells of the atrium including those of Miiller's papillae. It is 

 possible, of course, that Weiss' interpretation of these facts is correct, 

 and that the carmine found in these cells was in the act of being excreted 

 from the system into which it had been taken by the intestinal epithelium, 

 but on the other hand it may well be that the carmine entered the cells 

 concerned from the atrial cavity directly, in the same way that, according 

 to Weiss' view it must have entered the intestinal walls.* 



* Vide Weiss, Q.J. M.S., 31, 1890, p. 497 ; and Boveri, Zool. Jahrb., 5, 

 1892, p. 429. Goodrich, Q.J.M.S., 45, 1902, p. 493. 



