PERIPHARYNGEAL BAND, 



and occasionally the lips fuse in places so that the opening becomes sub- 

 divided into many (Ascidia marioni and atra, Phallusia mammillata). 

 The neural gland is said to be derived from a portion of the cranial vesicle 

 of the larva, which as is well known acquires a secondary opening into 

 the anterior end of the alimentary canal. It is clearly glandular, but its 

 exact function is quite unknown. It has been supposed, without suffi- 

 cient reason, to be a renal organ. Its secretion is formed by the disin- 

 tegration of cells proliferated from its epithelium. 



The peripharyngeal band consists in dona of two ridges placed 

 close together and encircling the pharynx at the hind end of the 



~/7- 



~rtf 



fb 



B 



FIG. 6. .4 The region of the dorsal tubercle and of the anterior end of the dorsal lamina of a 

 oung dona intestinalis, from within. B Dorsal tubercle and peripharyngeal band of 

 Ascidia, diagrammatic (after Seeliger). df dorsal lamina ; fb,, fb anterior and posterior 

 ridges of peripharnygeal band ; }g dorsal tubercle ; fr groove of the peripharyngeal band 

 //, epibranchial groove ; ks gill-slits ; nd neural gland ; rz languet of dorsal lamina. 



prebranchial zone (Fig- 4, c). Of these the anterior is without 

 cilia (Fig. 6.4, fb,), while the posterior has cilia on its front side. 

 They enclose between them a groove which may be called the 

 per ibranchial groove. The anterior and smaller ridge forms a 

 complete circle, whereas the posterior ridge is incomplete ven- 

 trally, each side of it being continuous with the marginal ciliated 

 tract of the endostyle (Fig. 4, e). Dorsally the posterior ridge 

 is deflected backwards and joins its fellow (Fig. 6). The space 

 enclosed by this backwardly deflected part of the posterior ridge 



