146 WILLIAM RAY ALLEN. 



EXPLANATION OF PLATE III. 



FIG. 5. Cross section of ridges on contiguous surfaces of labial palps (Fig. 40, fs) 

 showing their several positions. While a is uppermost (as in II and /// ) material is 

 carried mouthward; when p is raised by the erection of the ridge (as in 7) the stream 

 is reversed toward the posterior, and the cilia a no longer function. 



FIG. 6. (Slightly diagrammatic.) Cross section of the ciliated organs con- 

 cerned with food collecting; showing how the labial palps (Ip) by occupying several 

 positions in the mantle chamber, may or may not receive the material collected at 

 A". As a matter of fact, the palps can span almost the entire width of the mantle 

 chamber at this point, but the width is exaggerated here to show details with greater 

 clearness. 



FIG. 7. (After Posner.) Cross section of the edge of inner gill; showing the 

 groove (tr) by which material is transported toward the palps. 



Abbreviations. 



I, ridge erected; current reversed, m, mantle. 



11-111 , normal position of ridges, mf, cilia at bottom of furrows, 



A, anterior, P, posterior, 



a, cilia directed anteriorly, p, cilia directed posteriorly, 



/, foot, r, mucous accumulations of refuse 



gi, inner gill, material, 



go, outer gill, Ir, trough at margin of inner gill, 



ic, interlamellar chamber, A", points of convergence of ciliary 



Ip, labial palps, currents near labial palps. 



