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



similar to that of Physophora and the other Discolabidse, the cormidia being ordinate 

 and arranged symmetrically in a flat spiral line, which is twisted around the flat and 

 broad base of the shortened vesicular stem. (Compare PI. XII. figs. 7-9 ; fig. 7, dorsal 

 view ; fig. 8, lateral view, from the left side ; fig. 9, ventral view.) 



The ventral view (fig. 9) exhibits at once the bilateral form of the corm, which is 

 bisected in the ventral median line by the series of buds ; these develop from two 

 separate blastocrenes (springs of buds, or " puncta vegetationis "). The superior 

 blastocrene (ib) is the point of development of the nectosome (bracts), and from it 

 radiate bilaterally the ridges which bear the pedicles of the bracts. Each convex ridge 

 is composed of four finer parallel ribs ; these are straight and horizontal in the uppermost 

 and oldest ridges, undulating and vertical in the youngest and lowermost ridges. There 

 are five or six quadripartite ridges on each side of the trunk of the nectosome, divergent 

 from the ventral towards the dorsal side, where the large ovate pneumatophore arises. 

 The inferior blastocrene (fig. 9, is) is the punctum vegetationis of the siphosome ; 

 its numerous buds, densely crowded in the lower half of the ventral median line, 

 become so developed and dislocated that the superior compose a corona of palpons (q), 

 the inferior a basal corona of gonostyles (g) and alternating siphons (s) and tentacles (t). 

 The arrangement of these parts in the lateral view of the corm, after removal of the 

 majority of the palpons (fig. 8), seems to demonstrate that the cormidia, although densely 

 crowded without interval, are nevertheless ordinate. Each cormidium seems to be 

 composed of a large siphon, and the appertaining tentacle, of two gonodendra (a male 

 and a female group of gonophores), and of a certain number of palpons. Further, each 

 cormidium of the siphosome seems to belong to a corresponding quadripartite ridge of 

 the nectosome, with four parallel ribs bearing a number of bracts (figs. 8, 9, bp). 



Respecting the phylogenetic origin and development of this peculiar arrangement, 

 we may assume that originally each ridge of the nectosome (with a group of bracts), and 

 each cormidium of the siphosome, have arisen from a single medusome, the former from 

 its umbrella, the latter from its manubrium ; both being widely dislocated afterwards. 

 But in these ordinate cormidia of the Anthophysidse, as well as in the similar ones of 

 the Discolabidae and Nectalidse, a further comparative morphological study is required 

 to solve the difficult question of their original composition. 



Pneumatophore. — The float filled with air occupies the upper half of the ccenosome, 

 and is usually ovate or ellipsoidal. Its uppermost part is sometimes prominent over the 

 corona of bracts, at other times retracted and hidden between them. Its apex usually 

 bears a pink or purple pigment-star with eight rays, composed of elegant polygonal 

 exoderm cells (figs. 5-9). The centre of this star is usually colourless. The pneumato- 

 saccus includes the thin-walled chitinous pneumatocyst. Its lower part is connected 

 by a variable number of radial septa (usually eight or sixteen) with the pneumatocodon or 

 the outer wall of the float (fig. 7, p). 



