THE LIFE-HISTORY OF NUCULA DELPHTNODONTA. 353 



Leaving the ventral end of tlie stomachy the intestine bends 

 dorsally, and follows the posterior walls of the stomach nearly 

 to its dorsal end. Here the loops already described are 

 formed. From the loops the intestine passes posteriorly 

 ventral to the heart, bends around the posterior side of the 

 posterior adductor muscle, and opens in the mantle chamber. 

 It is composed of short ciliated cells that stain deeply. Its 

 lumen varies greatly in size, according to the amount of 

 matter it contains. 



Labial Palps. 



Soon after the embryo acquires its second gill lobe the 

 epithelium around the mouth, and for a short distance along 

 the sides of the body, becomes ciliated (fig. 41). This cilia- 

 tion precedes the formation of the palps, and, to a certain 

 extentj marks out the region where they will form. The 

 cilia are more numerous immediately anterior to the mouth 

 than they are immediately posterior to it, and they soon extend 

 along the sides of the body for about half the width of the 

 foot. The position of the ciliated patches on the body-wall 

 is such that the dorsal portion of each tends to lie horizon- 

 tally, and the ventral portion tends to the vertical position 

 (fig. 62, Ip.). The groove thus formed becomes the groove 

 betAveen the outer and the inner palps. The portion above 

 the groove forms the outer palp, and that below the groove 

 the inner palp. This is accomplished by the growth and 

 folding of the body-wall. The outer palp begins to grow 

 first, and in such a way that the line marking the dorsal 

 limit of the cilia becomes the free margin of the palp. This 

 leaves the inner surface of each outer palp covered with cilia, 

 and the outer surface unciliated. The two outer palps are 

 continuous anterior to the mouth, where they form a slight 

 ridge (figs. 5i and 63). 



For some time after the outer palps form folds, the inner 

 palps are represented by ciliated ridges (fig. 54), that reach 

 some distance beyond the posterior ends of the outer palps. 

 These ridges grow so that the lines marking the ventral limit 



