APPENDIX B. 



DESCRIPTION OF THE DORSAL TUBERCLE OF A LARGE SPECIES 

 OF ASCIDIA FROM KERGUELEN ISLAND. 



Amongst the Simple Ascidians from Kerguelen Island (January 20, 1874 ; Station 

 149d ; lat. 49° 28' 0" S., long. 70° 13' 0" E. ; depth, 28 fathoms ; bottom, volcanic mud; 

 surf. temp. 41°), I found a fragment, consisting of very little more than the test, of a 

 very large specimen evidently belonging to the genus AscicUa. On account of its very 

 imperfect condition, and of the absence of almost the whole of the body proper, it seemed 

 useless to attempt to refer this fragment to its proper species ; and as there was nothing 

 unusual about the appearance of the test, there was no reason to describe it as a new 

 species. Since the publication of the first part of this Report, however, on re-examining 

 this large specimen I found some fragments of the mantle and branchial sac and other 

 organs attached to the test in the region of the branchial siphon. Amongst these the 

 dorsal tubercle attracted my attention as being in a most remarkable condition ; so it 

 was cut out and sectionised, with the results given below. I note the condition of the 

 other parts so far as they could be made out, so as to aid in the future identification of 

 the species. The specimen was probably between nine inches and a foot or so in length. 



The Test is thick and cartilaginous. It is of a yellowish-grey colour. 



The Mantle is strong and muscular. 



TJie Branchial Sac is thick. The transverse vessels are closely placed, and all 

 of the same size. The internal longitudinal bars are strong, and bear very large 

 expanded papillae at their intersections with the transverse vessels (PI. XL fig. 13). 

 The meshes are much elongated transversely, so as to be five or six times as long as 

 they are broad. The stigmata are numerous and rather small. They are arranged 

 very irregularly, and there is a certain amount of minute plication in the wall of the 

 sac (PI. XL fig. 13). 



Tlie Branchial Siphon is short, and there is only a very narrow zona prse- 

 branchialis. 



The Tentacles are rather short and are not numerous. Their arrangement is 

 disturbed in the middle line dorsally by the enormous development of the dorsal 

 tubercle (PL XL fig 7), 



Tlie Dorsal Tubercle has the form of a large transversely elongated sausage-like 



