ANATOMY AND DEVELOPMENT. 1 85 



well-defined groove with white glistening walls, which is 

 the endostyle. The groove of the endostyle is deeper here 

 than in Amphioxus, but its epithelial walls have the same 

 histological differentiation, with the two rows of gland- 

 cells on each side of the middle line, the latter being: 

 occupied by a median group of cells carrying very long 

 cilia. The food which enters the mouth together with the 

 water does not pass out of the pharynx into the atrial 

 chamber, but is caught up by the slime secreted by the 

 endostyle and is then c^xxxeA forivards along the endostyle, 

 and, having arrived at the anterior extremity of the latter 

 at the base of the buccal tube, is carried round along a 

 circular ciliated groove which surrounds the base of the 

 mouth at the entrance to the branchial sac, until it reaches 

 the dorsal side of the animal, when it is led backwards by 

 the ciliary action of the cells of the dorsal lamina in the 

 form of a cord of slime in which the food-particles (micro- 

 scopic organisms, vegetable debris) are imbedded. 



The ciliated groove round the base of the buccal tube 

 connecting the anterior extremity of the endostyle with the 

 dorsal lamina is known as the peripharyngeal band or 

 pericoronal groove. We have already made the acquaint- 

 ance of the horaologue of this structure both in Amphi- 

 oxus and in Ammocoetes. It forms a complete circle 

 round the base of the buccal tube and is indicated in 

 Fig. 94 by the black hne which limits the pharyngeal 

 wall anteriorly. It is still better shown in Fig. 96, which 

 represents a young individual of Clavelina. 



The cord of slime containing the food passes backwards 

 along the dorsal lamina to the opening of the oesophagus, 

 which lies near the posterior end of the branchial sac, in 

 the dorsal middle line, through which it passes into the 

 stomach. The dorsal lamina is continued to one side of 



