igos.l EXCRETORY ORGANS OF METAZOA. 559 



ered an excretory organ (Hamann, 1887, Sarasin, 1888, Ludwig, 

 1889) and proved to be so by carmine injection (Kowalevsky, 

 1889), while to it has also been ascribed the function of producing 

 coelomic cells (Leipoldt, 1893). It is a slender axial sac, the oral 

 end of which ends blindly, opening by a delicate canal under the 

 madreporite close to the stone canal ; it is composed of a meshwork 

 of trabeculae of connective tissue, covered internally by an epi- 

 thelium, in the meshes of which lie amoeboid cells (Ludwig). 

 Hamann described its cavity as communicating with blood lacunae 

 and the Sarasins as connecting with the body cavity by nephro- 

 stomes, but these results have not been confirmed and the bulk of 

 evidence points to its being closed from other body cavities. 



Ophiuroidca. — Here both respiration and excretion take place 

 osmotically through the walls of the genital bursge (Cuenot, 1888). 



Asteroidea. — By injection Kowalevsky (1889) found that the 

 bodies of Tiedemann are the excretory organs of the ambulacral 

 system. Cuenot (1901) distinguished (i) amoebocytes, floating 

 cells in the coelom, blood vessels and ambulacral system, that are 

 first phagocytic, and when they become laden with excretory prod- 

 ucts leave the organism by passing through the walls of the gill 

 sacs; and (2) nephrocytes. Of the latter he distinguished: those 

 that take up indigo (epithelium of the intestinal cseca), and those 

 that ingest carmine (peritoneum, epithelia of perihaemal spaces and 

 ambulacral vessels, inner cells of septal organs). 



Holothiirioidea. — In the Synaptids the " ciliated funnels " have 

 been proved to collect waste products, by their ciliary action and 

 agglutinating secretion ; such products and amoebocytes loaded with 

 them become caught in these organs, and ultimately make their way 

 through the solid tissues to become deposited beneath the skin 

 (Schultz, 1895, Cuenot, 1902). These funnels are generally ar- 

 ranged in rows on either side of the mesenteric radix, and project 

 into the coelom either separately or in groups. Each is a some- 

 what spoon-shaped, flattened prominence, with a concave ciliated 

 surface, attached to the wall of the coelom by a slender stalk, both 

 plate and stalk being composed of solid connective tissue covered 

 by peritoneum. Thus they are really not funnels at all, but solid 

 projections into the body cavity, and cannot in any way be compared 



