SOME ASCIDIANS FROM THE ISLE OF WIGHT. 121 



tlie posterior end of the body. The intestine is narrow and uniform ; 

 its first bend is well in front of the cloacal siphon, its anterior wall 

 being on a level with the ganglion ; the second bend of the intes- 

 tine is behind the cloacal siphon, its posterior wall being on a level 

 with the opening of the oesophagus into the pharynx ; the rectum 

 is directed obliquely forwards towards the cloaca. 



Upon opening the pharynx from end to end, along the line of 

 the endostyle, the remaining structures can be examined. 



The coronal tentacles are forty or more in number. In an indi- 

 vidual possessing forty tentacles, they were of three sizes and 

 regularly arranged — ten long and slender primaries, ten inter- 

 mediate secondaries, and twenty short tertiaries. 



The prsehranchial zone is studded with microscopic papillae. 



The aperture of the dorsal tubercle is crescentic in the smaller 

 specimens, horse-shoe shaped in the individual represented in fig. 1, 

 the horns not being incurved. 



An epipharyngeal groove extends along one-third of the distance 

 between the dorsal tubercle and the ganglion, which is situated 

 half-way between the mouth and the cloacal aperture. The ganglion 

 is small, three times as long as broad, and extends over three of 

 the meshes of the pharyngeal wall, beginning at the fourteenth 

 horizontal bar. The epipharyngeal groove becomes elevated towards 

 it posterior end, and behind it commences the dorsal lamina, which 

 is very narrow, strongly ribbed transversely, and pectinated at its 

 margin. The ribs and teeth of the lamina correspond in number 

 with the horizontal bars of the pharyngeal wall. Occasionally there 

 are minute projections from the edge of the lamina which alternate 

 with the teeth in position. The concave side of the lamina shows a 

 series of weak ridges running towards its edge very obliquely from 

 before backwards. 



Branchial apparatus. — A portion of the inner face of the pharyn- 

 geal wall is shown on PI. VI, fig. 4. The horizontal vessels form 

 three complete series and a rudimentary growth. The primary 

 vessels {h. v. 1), which give off branches* to the body-walls, are 

 usually of greater diameter than those of the remaining series. 

 Between each pair of primaries are situated one secondary vessel 

 {h. V. 2), and two tertiary vessels {h. v. 3), at approximately equal 

 distances. 



Connecting ducts (c. d.) arise from all these vessels and support 

 delicate internal longitudinal bars (i. I. b.) which are surmounted at 

 the points of junction by moderately stout conical papillae (p,) and 

 at intermediate points by comparatively slender ones (i. p.). The 



* The origin of these branches — the dermato-branchial connectives — is marked in some 

 speclmeus by white spots upon the primary horizontal bars. 



