594 



THE INVERTEBRATA 



are transverse and longitudinal bars. The inner surface of this basket 

 work is crossed by internal longitudinal bars, slung from it and bearing 

 papillae which project into the branchial cavity. All the bars of this 

 apparatus are hollow and contain blood. The epithelium which covers 

 them is ciliated, the cilia being longer on the sides of the stigmata. 

 Ventrallythe basket-work walls are separated by a narrow, longitudinal, 

 imperforate tract known as the endostyle. This is folded into -a groove 

 (Fig. 446) lined by an epithelium which is glandular and ciliated in 

 alternate longitudinal strips, arranged in a manner similar to those in 

 the endostyle of Amphioxus. To right and left a ciliated strip runs 

 beside the groove. Posteriorly the groove passes into a caecum and 



.'/" 



Fig. 445. Portions of the pharyngeal wall of Ciona intestinalis. From Sedg- 

 wick, after Vogt and Yung. A, From within. B, From the outside, a, in- 

 ternal longitudinal bar; b, transverse bars of the first order; c, transverse 

 bars of the second order ; d, papillae ; e, transverse bars of the third order ; 

 /, /', stigmata. 



the lateral ciliated strips curve up, as the retropharyngeal band, to 

 the opening of the oesophagus, which is dorsal at the hinder end. 

 Anteriorly, the same strips are continuous with the posterior peri- 

 pharyngeal ridge, on each side of a gap in the latter. Dorsally, the 

 lateral walls are separated by a hyperpharyngeal band, from which 

 there hangs down into the branchial cavity a row of processes, the 

 languets, which are curved to one side. 



The stigmata lead, not directly to the exterior, but into a cavity, the 

 atrium, which opens externally at the atrial opening, is lined by ecto- 

 derm, and is placed dorsally like a saddle upon the branchial chamber, 

 surrounding the latter completely except (a) in front, and (b) in the 

 median line ventrally, posteriorly, and for a short distance from the 

 front end dorsally. The atrium is crossed by vascular trabeculae from 



