REPORT ON THE TUNICATA. 



21 



In Pyrosoma there are from twenty to fifty transverse vessels, and about the same 

 number of slits, which are usually about equal in breadth to the thickness of a vessel. 

 The internal longitudinal bars are from fifteen to thirty in number on each side. They 

 are ciliated on their edges. The meshes formed by the intersection of the transverse 

 vessels and the internal longitudinal bars are generally elongated transversely, and are 

 about three times as long as they are broad (see PI. I. figs. 17, 19). 



At the anterior end of the branchial sac is found the peripharyngeal groove, 

 bounded by the two peripharyngeal bands (PI. I. figs. 18, 19, pj:).). 



The endostyle runs along the ventral edge of the branchial sac in the usual manner. 

 It is very regular in its course (Fig. 4, en.). 



The dorsal lamina on the opposite edge of the branchial sac is in the condition of a 

 series of finger-like languets, having blunt points and ciliated on their anterior edges. 

 It is a curious fact that the dorsal languets are fewer in number than the transverse 

 vessels of the branchial sac, and appear to bear no definite relation to them. 



. ,^ qem. 



Fig. 4.— a single Ascidiozooid of Ptjrosoma, lying in the test, seen from the right side. 



at. atrial aperture, at.m. atrial muscle, hr. branchial aperture, hr.s. branchial sac, cm. mass of phosphorescent 

 cells, en. endostyle, gem. young bud on g.st. gemmiparous stolon, h. heart, i.s. inner surface of colony, /. languet, 

 m. mantle, m.h. muscle band, n.g. nerve ganglion, a\ oesophagus, ov. ovum, p.hr. peribranchial cavity, p.p. peri- 

 pharyngeal bands, st. stomach, s.gl. subneural gland, (. test, tcs. testis, t.p. process of test, tn. large ventral 

 tentacle, :. zona prebranchlalis. 



