. The British Tunicata; an unfinished monograph. Sea squirts; Tunicata. ANATOMY AND PHYSIOLOGV. 47 disposed in regular traiisverse series between the transverse channels. The coiled vessels do not so frequently intercom- municate as they do \nMolgida; consequently the stigmata are much longer, being less interrupted. The radiating vessels are not numerous, and they pass from the centre of. the coil to the transverse channels. The longitudinal bars are more rigid and cord-like than usual; they project considerably from the surface of the gill; and the papillfe which are at- tached to them are n
. The British Tunicata; an unfinished monograph. Sea squirts; Tunicata. ANATOMY AND PHYSIOLOGV. 47 disposed in regular traiisverse series between the transverse channels. The coiled vessels do not so frequently intercom- municate as they do \nMolgida; consequently the stigmata are much longer, being less interrupted. The radiating vessels are not numerous, and they pass from the centre of. the coil to the transverse channels. The longitudinal bars are more rigid and cord-like than usual; they project considerably from the surface of the gill; and the papillfe which are at- tached to them are not elevated, but inclining backwards are united throughout their length, and give support to wide membranes that extend from the surface of the transverse vessels. In this species the oral lamina is replaced by a series of well-developed filamentous processes. The most perfect, however, of the spiral type of gill is found in Molgula areiiosa. In this interesting species the interior of the branchial sac is furnished 011 each side with six or seven wide, longitudinal, ribbon-like bands, which are attached by. FIG. 7.—Tentacles of Ascidia Alderi. Highly magnified. one edge to the ti-ansverse vessels at the points where they cross them. These bands, how like soever in general appear- ance, are not to be confounded with the branchial folds in Stye-la and Molrjula ; they are the homologues of the longitu- dinal bars so constantly present, and with the transverse vessels give to the surface a coarse reticulation, the square meshes of which are each occupied by a conical eminence. On account of the prominence of the longitudinal bands these eminences, which look like so many miniature beehives, seem to be arranged in six or seven longitudinal series. Each cone is formed of a double spiral coil of secondary vessels united at the apex ; the coils are .perfect, and the stigmata, which are coextensive with them, appear to be scarcely, if at all, inter- rupted by intervascular communicat
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