REPORT ON THE TUNICATA. 69 



spindle-shaped bundle. These fibres are usually of a clear yellow colour, and at the ends 

 they become continuous with a very long delicate transparent fil.re, which runs usually 

 for a great distance through the mantle, and may either die away or may join a similar 

 filament from another bundle. The whole arrangement is rather suggestive of a muscle 

 with a belly and two long tendons as seen in higher vertebrates. 



The chief features in the branchial sac of Molgula are the distinct folds and the more 

 or less curved stigmata arranged in infundibula. 



The alimentary canal is always situated on the left side of the branchial sac, and has 

 one of the genital glands in its neighbourhood, the other being placed near the centre 

 of the opposite side of the mantle, and always anterior to the sacdike renal organ 

 (PI. IV. fig. 7). 



The Challenger collection contains six species of this genus, four of which were nev. 

 to science. 



Molgula gigantea, Cunningham (sp.) (PI. IV. figs. 1-4). 



Cynthia gigantea, R. 0. Cunningham, The Nat. Hist, of the Straits of Magellan, Edin. 1871. 

 Cynthia gigantea, R. O. Cunningham, Notes on the Reptiles, &c., obtained during the voyage of 



H.M.S. " Nassau," Trans. Linn. Soc., vol. xxvii. p. 489. 

 Molgula gigantea, Herdman, Preliminary Report, part iv., Proc. Roy. Soc. Edin., 1880-81, p. 234. 



External Appearance. — The body is oblong or oblong-ovate in shape, often cylindri- 

 cal, and usually compressed laterally. The anterior end is usually narrowish, but truncated 

 and flat. The posterior is rounded, usually broader than the anterior, and sometimes 

 irregular ; the dorsal and ventral edges are gently convex, and about erraal in length. 



The apertures are both at the anterior end ; they are moderately distant, conspicuous, 

 and slightly projecting. The branchial is at the ventral edge of the anterior end, on a 

 distinctly sixdobed teatdike projection, and usually bent so that the aperture joints 

 ventrally and somewhat posteriorly. The atrial is at the dorsal edge of the anterior end ; 

 it is not so prominent as the branchial, is four-lobed, and directed more or less anteriorly. 



The surface is even and moderately smooth in the upper part. The lower half is 

 thickly incrusted with sand attached to fine hair-like processes of the test. 



The colour in the upper part is usually a pale slate-blue. 



Length of body (antero-posterior) in a specimen of medium size, 19 cm. ; breadth of 

 body (dorso- ventral), 10 - 5 em. ; thickness of body (lateral), 7'5 cm. 



The Test is coriaceous, and rather thin but tough; it is opaque, and smooth in the 

 upper (anterior) part, but bears hairs on the posterior part, to which sand grains are 

 attached, forming an incrusting coat. 



The Mantle is thick ; and the musculature is strong, especially along the dorsal and 

 ventral edges. 



