672 THE INVERTEBRATA 



the pharynx, with a groove between them. In the dorsal middle line 

 of the prebranchial zone stands the dorsal tubercle. This is the pro- 

 tuberant, horseshoe-shaped opening 0^2. ciliated funnel v^hich. receives 

 the duct of a subneural glatid that lies under the brain. The function 

 of the gland is unknown. The funnel is innervated from the brain and 

 is supposed to be sensory. 



The rest of the pharynx constitutes the spacious branchial chamber. 

 The lateral walls of this chamber consist of a basket work, formed by 

 the subdivision of the original gill clefts. The openings of the basket 

 work (Fig. 470) are known as stigmata. They are longitudinally 

 elongate and stand in transverse (dorsoventral) rows. Between them 

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



Fig. 470. 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 ; 6, transverse bars of the first order ; c, transverse bars 

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

 /, /', stigmata. 



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. 

 Ventrally the basket-work walls are separated by a narrow, longi- 

 tudinal, imperforate tract known as the endostyle. This is folded into 

 a groove (Fig. 471) 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 the lateral ciliated strips curve up, as the retropharyngeal 

 band, to the opening of the oesophagus, which is dorsal at the hinder 



