08 THE VOYAGE OF H.M.S. CHALLENGER. 



wise be the case. In Cirripaihes and Stichopathes the zooids on the basal portion of the 

 stem become so much reduced that they are only recognisable as discoidal swellings of 

 the ccenenchyma, presenting a median aperture. In such cases the tentacles appear to be 

 lost first, and subsequently the body of the zooid becomes more and more reduced, until 

 finally it is no longer recognisable. In Pteropathes fragilis the tentacles appear to be 

 lost in a definite order. In the normal zooid the sagittal tentacles are larger, and situated 

 at a much lower level than the other four. In spite of their size the sagittal tentacles arc 

 the first to be lost, and some distance from the apex of a branch the zooids have usually 

 only four tentacles. Still lower down these become lost also, and soon the zooid is no 

 longer recognisable. In the Antipathina? generally the tentacles appear to be lost before 

 the body of the zooid. 



An attempt to indicate the phylogenetic relationship of the Antipatharia must be 

 deferred until my account of the histology of the group has been completed. In the mean- 

 time it may be stated that there appears little evidence that the Antipathidae are such 

 deo-enerate forms as v. Koch has supposed. His views on the subject were based on a 

 study of Parantipathes larix, which in many respects is quite an exceptional form. At 

 first sight the irregularity in the length of the mesenteries of this species might appear 

 to support v. Koch's view, but if the view which I have taken of their origin and 

 homologies be correct, the shorter mesenteries must be regarded as imperfectly developed 

 rather than degenerate. It appears to me more probable that the Actiniaria have become 

 elaborated from a simple hexamerous type, having probably the bilateral symmetry of 

 Leiopathes, than that the Antipatharia have become degenerated from Hexactiniee with a 

 large number of mesenteries. Although Leiopathes gldberrima possesses twelve 

 mesenteries, whilst all other Antipathinse, so far as we know at present, have only ten, it 

 does not necessarily follow that the majority have lost two mesenteries and become 

 degenerate from a hexamerous type having six pairs or more. The available evidence 

 appears to point in the opposite direction. Six well-developed mesenteries (three pairs) 

 are present in all Antipathidse, whilst none have more than three fully developed pairs. 

 Cladopathes amongst the Schizopathinae has only three pairs of mesenteries in all. Next 

 come Antipathes, Antipatliella, and a number of other genera with five pairs, two of 

 which are short and apparently not fully developed. The two additional pairs arc 

 situated one on each side of the transverse mesenteries which bear the reproductive 

 organs. That it is to say, in AntiiJathes, &c, there are four lateral compartments on 

 each side of the stomodaeum, whereas in Cladopathes there are only two. Finally, in 

 Leiopathes two opposite compartments bordering the transverse mesenteries become 



