576 MONTGOMERY— MORPHOLOGY OF THE [April 24, 



Anal Tubes. — There is one pair of these opening into the most 

 posterior portion of the intestine. On their surfaces there are 

 numerous " Wimpertrichter," and Greef supposed these not to open 

 directly into the ccelom, but Spengel demonstrated that they do make 

 such a direct connection and that their ciHated lining is continuous 

 with the peritoneum. Their function is not ascertained. From 

 their position Spengel concluded them to be ectoblastic, but not to 

 be homodynamous with the segmental organs. But Hatschek 

 (1880) describes them as arising not from the rectum but from the 

 somatic mesoblast of the telson ; and according to this account they 

 form first the Wimpertrichter, then later the external pores that lie 

 lateral from the anus. 



Larval Nephridia. — These are known only from Hatschek's ac- 

 count (1880) of Echhinis; the first origin of these " Kopfnieren " 

 was not determined; each becomes a much branched organ with 

 intracellular cavity, from the surface of which delicate blind capil- 

 laries grow out. Torrey (1903) was unable to find larval nephridia 

 in Thalasscma, and determined that in this form excretion is accom- 

 plished by certain mesenchyme cells. 



21. Myzostomida. 

 The single pair of nephridia were first recognized as such by 

 Beard (1894), and their structure particularly described by Wheeler 

 (1896) and Stummer-Traunfels (1903). Their relations differ 

 somewhat in different species: they may be separated from each 

 other, or their open and large nephrostomes may be united, their 

 nephridiopores may be separated or united ; in one species nephro- 

 stomes appear to be absent. In some species they are purely excre- 

 tory, in others also spermiducal. From their development Wheeler 

 concluded that they originally opened on the surface of the body and 

 not into the cloaca (their usual termination in the adult), because 

 in one species the unpaired excretory duct opens " on the surface 

 of the body through a papilla lying just ventral to the cloacal 

 orifice."^ 



^The segmental sacs (suckers) supposed by Nansen (1885) to be ne- 

 phric, have been shown by Wheeler to be probably sensory. 



