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



polygonal cells. The dilated basal part presents eight longitudinal stripes, the external 

 insertions of the eight radial septa which divide the pericystic cavity of the pneumato- 

 phore into eight radial pouches. 



Nectophores (figs. 1, 4, lateral view; figs. 2, 3, dorsal view). — The nectocalyces are 

 broad and short, truncate, conical in the tapering distal or basal part, provided with a 

 pair of large auricles in the dilated apical or proximal part. The frontal axis of the 

 latter is three times as long as that of the former, and twice as great as the principal 

 and the sagittal axis. The principal axis is directed obliquely from above and within 

 downwards and outwards. The upper or dorsal face is emarginate convex ; the lower 

 or ventral face concave, with a median groove, from which arises the short triangular 

 pedicle attaching the nectophore to the trunk. The two lateral auricles or apical wings 

 are nearly square, slightly bilobate on the lateral edge, and embrace the trunk in the 

 middle interval between two nectophores of the opposite series (an upper and a lower). 

 Each of the two paired wings is nearly as large as the odd basal part of the nectophore. 



Nectosac (figs. 1-4). — The subumbrella of the nectophores has nearly the same form 

 as the surrounding exumbrella, from which it is separated by a rather thin but firm 

 jelly-plate. The two lateral auricles, however, are more deeply emarginate in the 

 former, nearly bilobate. The four radial canals are, as usual, of very different size 

 and form ; the two sagittal simply curved in the sagittal plane (the dorsal about twice 

 as long as the ventral) ; whilst the two lateral vessels (right and left) are much longer, 

 and exhibit a complicated undulating course (with four loops), which is intelligible by 

 comparison of figs. 3 and 4 (compare above, p. 216). 



Siphosome (fig. 1). — The axial trunk of the siphosome is a slender and exceedingly 

 contractile cylindrical tube, many times longer than the trunk of the nectosome. It has 

 in the fully expanded state a length of 200 mm. or more, and is therefore ten times 

 as long as in the strongly contracted state, when it is only 20 mm. long. The corm 

 contracts very suddenly, and passes over rapidly from the former into the latter state. 

 The entire trunk is densely covered with innumerable prismatic bracts, and at regular 

 large intervals with a great number of ordinate cormidia. All the parts of the corm are so 

 hyaline and transparent, and for the most part so glassy and colourless, that the animal is 

 difficult to perceive, even in the fully expanded state and in motion. The swimming 

 power of the nectosome is great and the usual locomotion very quick. 



Cormidia (PI. XIV. fig. 1 ; PI. XV. fig. 5). — Each cormidium is composed of a 

 large siphon (s), with a tentacle (t), a peculiar cyston (y), a male gonostyle (h), and a 

 female (/), and a number of bracts, which compose a protecting cavity for the former 

 parts. Besides, numerous other bracts cover the long internodes between the cormidia, 

 which bear no other organs. 



Bracts (PI. XIV. fig. 1; PI. XV. figs. 5, b, 6, b, 10).— The hydrophyllia are extremely 

 numerous and of a peculiar form, difficult to perceive because of their glassy transparency, 



