MB. A. HANCOCK ON THE TUNICATA. 309 



On the Anatomy and Physiology of the Tunicata. 

 By Albany Hancock, F.L.S. 



[Bead June 20, 1867.] 



Hating employed myself recently in the investigation of the 

 Tunicata (their anatomical structure and physiology) with a view 

 to a monograph of the British species, which my late lamented 

 friend Mr. Alder and I had undertaken to prepare for the Ray 

 Society, some very interesting anatomical facts have come to 

 light ; and I now propose to give a succinct account of the more 

 important of these, believing that they cannot fail to be acceptable 

 to those naturalists who may have studied these low but not by 

 any means unattractive moUusks. I reserve, however, for some 

 future occasion a more complete and detailed description. 



When I took up this subject, I had little expectation of meet- 

 ing with much that was new ; for perhaps in no other group of 

 the MoUuscan subkingdom hast he anatomy been so frequently 

 and so ably investigated as it has been in the Tunicaries ; and, 

 indeed, in them, all the leading points appear to have been fully 

 determined ; but experience proves, nevertheless, that much of 

 interest has been left unobserved, quite suificient to reward the 

 labour of reexamination, and seemingly ample enough to modify 

 some of the more important morphological determinations. 



This unexpected result may, in part, be owing to the fact that, 

 while my researches have been chiefly confined to the simple 

 Ascidians, it is apparently to the compound, social, and pelagic 

 forms that the greatest attention has been hitherto given. Thus 

 it happens that numerous details have remained until now unno- 

 ticed in the former group. 



There is something fresh to record in nearly all the visceral 

 organs, but in none so much perhaps as in the vascular and 

 respiratory systems. Before entering, however, on such new 

 matter, it will be well to say a few words respecting the tunics, so 

 characteristic of these animals. In all the various forms that 

 have been examined, thei'e is no great difficulty in determining 

 the presence of three tunics, or envelopes — namely, the test or 

 outer tunic, the mantle or inner tunic, and the lining membrane 

 or inner tunic of Prof. Huxley.* The lining membrane and 

 mantle are always, to a greater or less extent, adherent to each 



* This tunic was first pointed out by M. Milne-Edwards, in his work on the 

 Ascidies composees, p. 54. 



LINN. PBGC. — ZOOLOGT, VOL. IX. 25 



