548 MONTGOMERY— MORPHOLOGY OF THE [April 24, 



entered upon. I have endeavored to consult all the more important 

 literature up to 1907, but at the same time to refer in the citations 

 to only the more comprehensive accounts ; the literature references 

 therefore do not by any means represent complete bibliographies, 

 but refer the reader to the more important memoirs. 



The Orthonectida, Dicyemida, Cnidaria and Fori f era lack special 

 excretory organs ; and such structures are still unknown for Cephalo- 

 discus, Rhahdopleura, the Chaetosomatidas, Desmoscolicidse, and 

 Pentastomida. 



I. Ctenopiiora. 



Here there are short, presumably entoblastic, canals that connect 

 the aboral canal (funnel canal) of the gastro-vascular cavity with 

 the aboral surface of the body; there may be two or four of these 

 openings; these discharge injected carmine, while there is no evi- 

 dence that water is taken in through them (Chun, 1880). 



2. Plathelminthes. 

 These possess branching, tubular organs whose finest branches 

 (capillaries) have intracellular cavities and terminate in closed 

 flame cells, the latter being very small and numerous. Nothing is 

 known as to their embryonic origin, except the one observation of 

 Lang (1884) that in Polyclades a pair of solid ingrowths of the 

 ectoblast seems to represent their beginnings. The main structural 

 variations are with regard to the number, ramification and degree 

 of anastomosis of the main canals, and the number and position of 

 nephridiopores and excretory canals. 



( I ) Tiirbellaria. 



Polycladidea. — Discovered by Max Schultze (1854) these organs 

 have received subsequent description only by Lang (1884), who 

 found that the terminal flames are unicellular and who could trace 

 the supposed excretory canals of TJiysanozoon to the dorsum, but 

 could not find their openings there. Accordingly, a complete 

 knowledge of their structure is still a desideratum. T have not 

 been able to find them on sectioned material. 



Rhabdococlida. — Here they appear to be absent onlv in the 



