234 WILLIAM RAY ALLEN. 



(a) The Role of the Labial Palps. 



The writer has checked the matter as carefully as possible, and 

 believes that there is ground for the views of both Wallengren 

 and Siebert. The details of arrangement may not correspond 

 exactly in the several species. On the lower half of the palps the 

 cilia under consideration usually strike downward, and those of 

 the tipper half strike upward. Thus the lighter and finer particles 

 tend to be drawn upward and forward as food, while the heavier, 

 coarser, materials are more likely to be carried downward. The 

 differentiation of the mechanism corresponds pretty well to that 

 of the upper and lower portions of the ciliated surfaces of the 

 mantle chamber as a whole. It is impossible to make direct 

 observation of the streaming on any one ridge of the palps. But 

 where substances of varying fineness are placed together on the 

 palps, such as carborundum dust and carmine, there is a tendency 

 to assort them. The carborundum particles move along the 

 apices of the ridges and are carried nearly lengthwise of the palps. 

 The carmine gravitates farther into the furrows between the 

 ridges. Near the lower margin of the palps carmine is carried 

 obliquely downward and forward, and on the average reaches the 

 lower edge of the palps before the carborundum. When placed 

 on the upper portion of the contiguous palp surface, carmine is 

 drawn upward and forward to a greater extent than the car- 

 borundum, then forward toward the mouth. 



The respective upward or downward pull upon the carmine may 

 be accentuated by stretching the palps lengthwise, thus drawing 

 the ridges farther apart and exposing the cilia of the furrows to 

 a greater extent. 



Attempts were made to effect a reversal of the ciliary currents 

 of the furrowed surface of the palps by injections of curari, 

 strychnin, atropin, pilocarpine, and by electric stimulation. The 

 injections were made through the body wall into the sinuses near 

 the base of the palps. Observations were made at various in- 

 tervals from ten minutes up to several hours after injection. It 

 was never found possible to control the reaction. There was a 

 perceptible response to none of the several drugs except strychnin. 

 This sometimes caused a contraction, at other times a relaxation 



