627 



tempted to support it by the assumption that the presence of the ciHa 

 in the canal indicates that the canal itself is simply an invagination 

 of the ciliated apical surface of the cell, and that a means is thus 

 provided for bringing the nutritive fluid into close relation with the 

 blood sinuses at the base of the cell. He further held that the prob- 

 able function of the cilia in the apical end of the canal is to facilitate 

 the introduction of the nutritive fluid, and that the canal is the means 

 whereby greater intestinal surface and rapid absorption are insured 

 without consequent diminution or weakening of the intestinal wall. 



Vejdovsky ('06, p. 65) and Cejka ('10, p. 17) assign a secretory 

 function to these cells, and assume that the cilia aid in the passage 

 of the secretion from the canal into the lumen of the alimentary tract. 

 They also claim that the cells are produced by modifications of the 

 deeper-lying cells of the epithelium and that, in sections, intermediate 

 stages in such a development can be seen. 



We have made no observations which enable us to contribute 

 directly to the determination either of the function or of the mode 

 of origin of these cells, but have made some observations on the ar- 

 rangement of the cilia of the canals and offer some suggestions as 

 to their probable function. 



We have numerous sections of specimens from each of the species 

 of Fridericia herein described which show clearly that the cilia of 

 the canal are directed towards the opening at the apical end as rep- 

 resented by Vejdovsky, and have found no instance in which they 

 extend in the opposite direction as figured by Eisen ('05, PI. XVII 

 and XX). We believe that the cilia may have a function quite dif- 

 ferent from the one previously assumed. 



Experiments and observations by Cuenot, although not dealing 

 directly with this subject, throw light on the problem in an interest- 

 ing way. He has shown ('97, p. 105) that the vibratile cilia in the 

 nephrostome of the nephridium of Oligocliceta can not introduce the 

 cocloiiiic fluid into the interior of the nephridium except when inequali- 

 ties in the fluid pressure in the lumen will permit. Furthermore, he 

 has shown that solid bodies in suspension in the coelomic fluid can 

 not pass through the orifice of the nephrostome because the thickly 

 set cilia play the role of a sieve or filter and form an impassable bar- 

 rier to any solid particles, except possibly those which are excessively 

 minute. In view of these facts it seems probable that the prime 

 function of the cilia of the nephrostome is the prevention of the 

 passage of solid particles into the nephridial lumen rather than the 

 introduction of fluids into the lumen as has been assumed. 



It seems, then, reasonable to infer that the cilia in the apical part 

 of each chylus cell canal also function as a filter, preventing the in- 



