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



trunk of the siphosome in wide spiral turnings. Hence, it appears as though the axis 

 of the cone formed by the nectophores was only a lateral branch of the upper end of the 

 ccenosarc ; but in reality the upper part of the latter is deflexed and turned ai'ound the 

 lower part. The youngest and smallest nectophores, therefore, are placed at the upper- 

 most part, the oldest and largest at the lowermost part of the nectosome. The point 

 of vegetation of the former is very near to that of the siphosome, but separated from it . 

 by a small interval (PI. XXIX. fig. 7, x. Compare 35, p. 553, Taf. xlvii. fig. 27, ah). 



Nectophores. — The nectocalyces of the Polyphyidse appear in two different forms, 

 which are characteristic of the two subfamilies of this family. The Hippopodidae (sensu 

 stricto) have smooth nectophores, similar to a horse-shoe, with rounded surface (Hippo- 

 poclius and Polyphyes, PL XXIX. figs. 1-8); they may be derived from the Prayidse. The 

 Vogtidae, on the other hand, represented by the genus Vogtia (figs. 9-14), have pentagonal 

 nectophores with angular surfaces ; they may be derived from the Diphyopsidse. The 

 fundamental form is always bilaterally symmetrical, a deep ventral groove dividing the 

 nectophore into two equal halves. The jelly-substance is veiy voluminous and usually 

 hard, cartilaginous ; the nectosac is relatively very small and more or less rudimentary. 



The special form and the arrangement of the nectophores in alternately opposite 

 pairs are very peculiar. That part of the nectophore which bears the circular opening of 

 the nectosac must be regarded, of course, as the basal part. Opposite to this is the apical 

 part, or the true pedicle of the nectophore, a small triangular lamella, by which it is 

 attached to the common stem. This pedicle arises in the sagittal plane of the nectophore, 

 midway between the two parallel ventral wings, which include the deep concave ventral 

 groove. Strictly speaking, only the vertical inferior half of this axial groove, beyond the 

 pedicle, represents the ventral side, whilst its superior half, above the pedicle, belongs to 

 the dorsal side. The outer or abaxial part of this latter forms the free convex dorsal 

 face of the nectophore, which ascends more or less vertically in the lateral profile view of 

 the nectosome. Each nectophore embraces with the two lateral wings of the ventral 

 groove the adjacent parts of two other (superior) nectophores ; with the descending- 

 ventral part of the wing the same part of the opposite nectophore, and with the 

 ascending dorsal part of the wing the basal part of the superjacent nectophore of the 

 same side. An important consequence of this peculiar arrangement is, that the openings 

 of the nectosacs become hidden and nearly closed by the uppermost covering part of the 

 subjacent nectophore ; only the openings of the two lowermost (oldest and largest) 

 nectophores lie quite open, and are not covered. 



Nectosac. — The swimming cavity in the nectophores of the Polyphyidse is very small, 

 flat, and reduced, and the muscle-plate of its subumbrella very thin ; the power of 

 swimming therefore very weak. Indeed these Calyconectae swim more slowly than any 

 of the other groups of this order. The velum, too, which surrounds the wide opening of 

 the nectosac, is very small, usually crescentic or sickle-shaped, broader in the dorsal 



