102 BRITISH TUXICATA. 



a simple loop, the convexity downwards, and with the 

 right point a little prolonged, and there are about 

 twenty slender tentacular filaments at the base of the, 

 incurrent tube, pretty-regularly large and small alter- 

 nately. The nervous ganglion is nearly half way down 

 the mantle and is almost concealed by the gland in 

 connexion with it. 



The ovary is a much branched and dendritic organ 



J o 



spread over the left side of the intestinal loop ; and the 

 male caeca are apparently confined to the same side, 

 but are for the most part buried amidst the coating of 

 cellular matter. 



AscicUa nidi* bears a great resemblance to A. mentulu 

 in many of its characters, and may have been passed 

 over as a variety of that species. It differs, however, 

 in size and colour, in bearing small distant tubercles, 

 and in being much more largely attached. The anal 

 orifice, too, is, in the mantle, placed at the end of a 

 longish tube which enters into an internal sheath formed 

 by a thickening of the test, and is very little produced 

 outside ; the external opening varying in position 

 according to the length of the tube. In a variety from 



o O */ 



Hastings which we ow r e to the kindness of Mrs. Blackett, 

 the tube is very much elongated within the test, and 

 opens externally at a short distance from the branchial 

 aperture. Usually, however, it is situated about half- 

 way down the test, pretty near to the position that it 

 occupies in the mantle. Some varieties of this species 

 approach, in appearance, large specimens of Axrhlui 

 depressa. 



11. Ascidia venosa Midler. 

 (PI. VII, fig. 5 ; PI. VIII, IX, X; and fig. 4 in text.) 



Ascidia venosa MULLER Zool. Dan. Prod. [1776], p. 225, 

 no. 2736, and Zool. Danica, I [1788], p. 25, pi. xxv, 

 f. 13; [LAMARCK Anim. sans Vert. ed. 1, III (1816), 

 p. 125; ed. 2, III (1840), p. 532; BRUGUIERE] Vers, I 

 [1789], p. 154, pi. Ixv, f. 4-6, in Encycl. Meth. ; 

 [THOMPSON in Ann. Nat. Hist. (1) V (1840), p. 93;] 



