THE LIFE-HISTORY OF NUCULA DELPHINODONTA. 355 



mouth by a small ridge that occupies the position of an 

 upper lip. In the same way the inner palps are connected 

 by a ridge posterior to the mouth that is compai'able to a 

 lower lip. The corners of the mouth are continuous with the 

 space between the two palps of each side. The opposed 

 surfaces of the palps are densely ciliated, and thi'own into a 

 series of ridges and grooves that tend to lie opposite each 

 other on the two palps. Near the free margins this arrange- 

 ment may be considerably broken. Large blood-spaces 

 follow along these ridges. Each outer palp is supplied with 

 two grooved appendages that originate near its dorsal 

 margin. The most ventral of these appendages (fig. 48, pap.) 

 can be extended far beyond the margin of the shell, and is 

 used to elevate mud with the contained food. The dorsal 

 appendage sets over the anterior end of the groove of the 

 ventral appendage, and with it forms a short tube that opens 

 between the palps. Each ventral palp appendage is supplied 

 with longitudinal muscles (fig. 66, Im.), that are continued in 

 from the body-wall ; with a large nerve {x)n.) that originates 

 in a cerebral ganglion, and runs posteriorly along the united 

 dorsal margins of the outer and inner palps ; and with a 

 continuous blood-space {hs.). The epithelium lining the 

 groove of the append;ige is very thick, and is densely covered 

 with cilia. The nuclei of these epithelial cells are very long 

 and slender. The muscles in the palp appendages are so 

 placed that their contraction causes the appendages to curl, 

 as shown in fig. 48, pap. 



It is not easy to observe individuals of this species while 

 they are feeding, as they normally live entirely covered by 

 the mud. If specimens are placed in a dish of sea water, 

 in which there is only a thin layer of mud, the action of 

 the palp appendages may be observed. It is well to use as 

 much mud as possible without affording the animals an 

 opportunity to bury themselves, and to use specimens that 

 have not been in mud for several days and are accordingly 

 hungry. The mud is passed along the grooves of the palp 

 appendages by the action of the cilia, and finally conducted 



