560 MONTGOMERY— MORPHOLOGY OF THE [April 24, 



with tlie peritoneal funnels (peritoneal evaginations) of other 

 forms. In the Pedata.the respiratory trees have been considered 

 as in part excretory (Schultz, 1895) ; and the organs of Cuvier, 

 tubes that also open into the cloaca behind the preceding, have been 

 regarded as excretory by Herouard (1893), but it is proven that 

 these are rather eversible defensive structures (Minchin, 1892, 

 Russo, 1889). 



The ambulacral system of the echinoderms seems to mainly 

 subserve locomotion, respiration and nutrition ; but the bodies of 

 Tiedemann, as mentioned above, that occur in it are excretory, and 

 the Polian vesicle in holothurians may contain an " irregular non- 

 living mass of brown spherules " which may be waste substances 

 derived from the brown wandering cells occurring elsewhere in 

 this system (Gerould, 1896). 



The larvae lack nephridia, and there appear to be no organs in 

 this group comparable with excretory organs in others. The only 

 representatives of peritoneal funnels are ciliated evaginations from 

 the embryonic hydrocoel that join secondarily with ectoblastic in- 

 vaginations; there is usually only one of these and it persists as the 

 stone canal, but there may be two; Field (1892) compared the 

 enterocoels with nephridia that have secondarily come into the 

 service of locomotion. 



There is little known of the development of the genital organs 

 of Holothurioids. In Asteroids they have been described as coming 

 from a solid mesenchyme mass that invaginates the peritoneum ; 

 only in Echinoids is the gonad stated to be peritoneal, a proliferation 

 of cells of the left posterior enterocoel. Accordingly, there is no 

 evidence that the gonads or their ducts stand in relation to nephridia. 



15. TUNICATA. 



Special organs of excretion fail in the Appendicularias (Seeliger, 

 1893), ^"^^ ^ have not found them described for the Doliolidae. For 

 other forms Dahlgriin (1901) has distinguished the following 

 kinds: (i) Scattered excretory cells, in the visceral region (in 

 BntryUiis, Botrylloidcs, Polycyclus, Ciona, Salpa) ; (2) vesicles, 

 rather numerous in the connective tissue, each with a wall formed 

 of prismatic cells and with fluid or solid contents {Ascidiella, 



