244 F. W. GAMBLE, B.SC. 



pair of small, pointed tentacles. The dorsal surface is typically 

 covered with small coloured papillae — absent, however, in the variety 

 Icevigatus. Excepting the margins, the body is opaque. The ground- 

 colour is yellowish-white. The main-gut and its six pairs of branches 

 are brown, red, yellow, &c. In adult specimens they are largely 

 concealed by the genital organs, but reappear on the margin, where 

 their terminations are usually brightly coloured. The colour of the 

 dorsal tubercles is variable and due to pigment in the epidermis. 

 When the tubercles are absent their position is indicated by pigment- 

 spots. Thus the colour is due partly to the contents of the gut, to 

 pigment, and to the genital organs. Combinations of these three 

 sources of colour account for the diversity between individuals of the 

 same and of different ages, and appear to be correlated with the 

 substratum (generally species of Leptoclinum and other Ascidians). 

 Three to four black spots are present in specimens of the Icevigatus 

 variety, round the first pair of secondary gut-branches. (For good 

 descriptions of the appearance of this animal at different stages of 

 growth see Lang, pp. 54, 568 — 571). 



The mouth, just behind the brain, leads into a conical pharynx, 

 the apex of which is directed backwards and is continued into the 

 long main-gut. From this six lateral pairs of branches arise at right 

 angles, which, after branching and anastomosing freely, end in terminal 

 vesicles opening to the exterior through temporary epidermal pores at 

 the moment of the expulsion of feecal matter. The elongate cephalic 

 group of eyes borders the white area produced by the pharynx, and 

 extends forward beyond the brain. There is also a distinct group at 

 the base and on the ventral surface of the tentacles. The male genital 

 pore lies close behind the mouth, the female aperture halfway between 

 the anterior end and the subcentral sucker. The vesicula seminalis 

 is very large. The uterus is a large lobed sac surrounding the main 

 gut ; the uterine glands are numerous (10-11 on each side). Sur- 

 rounding the female pore is the very large radiate " shell-gland." 



Habitat. — On compound Ascidians and the sponge Hymeniacidon 

 sanguinea, 5 — 15 fms., Plymouth (W. Garstang, F. W. G.) ; Port Erin, 

 Isle of Man, 18 fms. (H. C. Chadwick). Var. Icevigatus between tide- 

 marks, Port Erin, and neighbourhood (W. J. Beaumont, F. W. G.). 



Distribution. — Naples (Lang). 



