PECULIAR TYPE OF NEPHRIDIA IN NEMERTEANS. 51 



direction, but probably pass mainly into the esophagus. Such a 

 disposition of these waste products need not occasion any sur- 

 prise when one considers how important a part the esophagus 

 plays in respiration. I have often observed a species of the 

 genus (Tceniosoma delineatum} with its mouth and esophagus 

 widely dilated, while the rhythmic contractions of the body walls 

 caused a comparatively large volume of water to be taken into 

 the esophagus and then discharged through the mouth. In this 

 manner the walls of the esophagus are constantly bathed with a 

 regularly changing supply of water. Excretory products poured 

 into the lumen of this portion of the alimentary canal would 

 thus be quickly discharged from the body through the mouth. 

 When, on the other hand, the esophagus is filled with food --a 

 large annelid, for example --the pressure on the esophageal 

 walls would very likely be sufficient to close up the nephridial 

 ducts opening into this cavity, and in such a case the efferent 

 ducts opening externally would be brought into service, and the 

 excretory products be discharged through them. 



The path from the nephridial canals to the esophageal lumen 

 is much more direct than that through the thick muscular walls 

 to the exterior of the body. Hence, with an abundant means 

 of constantly flushing out the esophagus in the act of respiration, 

 the animal economy is as well served by the discharge internally 

 as by a direct flow to the exterior. 



Only in such forms as have large mouths and use the esopha- 

 gus as a respiratory organ would this be the case, however. 



Although the two species mentioned are the only nemerteans 

 in which this peculiar condition of the nephridial ducts is known 

 to exist, yet in one other species of the same genus (Tceniosonia in- 

 dicum) Punnett * has found fine cords of cells resembling delicate 

 ducts, compressed so as to obscure the lumen, passing into the epi- 

 thelium of the esophagus, although no actual openings were found. 

 Neither did he find any ducts opening externally. And in some 

 of the other species, belonging to different genera where careful 

 study has as yet failed to recognize the efferent ducts, perhaps 



1 Punnett, R. C., " Fauna and Geography of the Maldive and Laccadive Archipela- 

 goes," Vol. I, part I, p. 105, 1 901. 



