88 THE VOYAGE OF H.M.S. CHALLENGED. 



border and tentacular zone ; from this arise (8) the numerous mantle-vessels of the 

 exumbrella, which form a dense network in the latter, and from these arise (9) the 

 mantle-vessels of the vertical crest, which form a dense network of different form on its 

 two sides ; four of these crest-canals are much stronger than the others, two opposite 

 longer, which run along the free upper edge of the crest, and two opposite shorter, which 

 bisect the triangular sides of the crest, and arise near the centre of the frontal groove ; 

 (10) a double series of elegant pinnate sail-canals, which arise from the large superior 

 edge-canal of the crest, and run in the soft sail border towards its free margin ; they are 

 here united by a small outermost canal running in the free edge of the sail. The special 

 form and reticulation of these numerous canals is about the same as figured by Alexander 

 Agassiz * in Velella (Armenista) mutica. 



Gonostyles (fig. 2 ; fig. 4, gs ; fig. 8, gs). — The small sexual siphons, or "gonoblastidial 

 polypites," are very numerous (many hundreds in the larger specimens) and densely 

 crowded, occupying the entire broad gonostylar zone between the base of the central siphon 

 and the corona of tentacles. Their upper or proximal half is cylindrical, and covered 

 with bunches of medusiform gonophores (g) ; their lower or distal half is a contractde 

 muscular stomach, beset with sixteen longitudinal rows of cnidonodes ; its proboscis 

 opens below by a very extensile mouth, and this is sometimes distinctly lobed (fig. 8, so). 

 The special form and structure of the gonostyles is the same as figured by Alexander 

 Agassiz 2 in Velella (Armenista) mutica. 



Tentacles (figs. 1-4, t). — The corona of tentacles, placed in the elliptical groove 

 between the outer edge of the gonostylar zone and the inner edge of the broad mantle- 

 border, is composed of two or three rows of tentacles ; those of the innermost row are 

 the largest, and in the expanded state about as long as the transverse diameter of the 

 umbrella. The tentacles of the outer row, alternating with the former, are only half as 

 long ; and when there is a third outermost row, these are very short. The form and 

 structure of these cylindrical tentacles are the same as in other Velellidaj ; they are beset 

 on both sides with two lateral rows of sessile cnidocysts. 8 



Armenista sigmoides, as described above from the Tropical Atlantic (Station 346), 

 is perhaps identical with a Velella of which I have obtained several specimens from 

 Cape of Good Hope, collected by Dr. W. Bleeck. The short description and the figures 

 which Eschscholtz (1) has given of Velella indica (also occurring at the Cape) are not 

 sufficient to decide the question of the identity of these species. Further accurate 

 examinations and comparative studies are required to enable a better distinction of 

 the different species of Disconectse. 



1 57, pis. iv., v. 2 57, pi. ii. 3 Compare Kolliker, 4 ; Vogt, 6 ; Huxley, 9 ; Agassiz, 57. 



