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



contracted state is three to four times as high as broad. Its height equals half the 

 height of the complete nectophore. Its dorsal face is more convexly vaulted than the 

 ventral, which is nearly in contact with the dorsal wall of the hydrcecium. The canal 

 of the nectophore (fig. 6), which arises from the constriction between somatocyst (cs) 

 and hydrcecium (ui), descends nearly vertically to the centre of the ventral median line 

 of the nectosac, and here gives off the four radial canals, which have very different lengths. 

 The shortest is the ventral canal of the nectosac (fig. 6, cv) ; it extends only through the 

 basal half of the nectosac. The longest, on the contrary, is the opposite dorsal canal 

 (cd) ; it runs from the basal circular canal (cc) along the whole dorsal side (in the dorsal 

 median line of the nectosac), and then from its top downwards through the apical half of 

 the ventral line. The two symmetrical lateral canals (ex right, and cl left) are equal and 

 form an S-shaped loop ; they ascend from the basal circular canal (cc) in the dorsal half 

 of the nectosac vertically, send off into its apical third a slender caecal sac (cy), and then 

 descend in the ventral half, meeting each other and the two other canals near to the 

 centre of the ventral line. 



The mouth of the nectosac (figs. 1, no, and 7, no, basal view; fig. 8, no, lateral view 

 from the right side) is surrounded by a broad velum (v) and armed with five serrate 

 teeth of nearly equal size, the odd dorsal tooth (fig. 8, nd) is perradial ; the two paired 

 dorso-lateral teeth (n 1 left, n 2 right) give off the two dorsal basal crests of the nectophore ; 

 finally, the two paired ventrolateral teeth (fig. 8, n 3 left, n 4 right) may be regarded 

 as separated branches of a forked (originally odd) ventral tooth. 



Hydrcecium (figs. 1 and 7, ui, basal view; fig. 2, ui, apical view; fig. 4, ui, ventral view ; 

 fig. 5, ui, lateral view from the left side ; fig. 6, ui, from the right side). — The hydrcecium 

 or the funnel cavity of the umbrella completely includes the retracted siphosome ; it is 

 slenderly campanulate or nearly cylindrical, and about as large as the nectosac, which 

 is placed at its dorsal side. The vertical main axes of these two organs are nearly 

 parallel ; but the apical half only of the hydrcecium is in immediate contact with the 

 basal half of the nectophore, whilst the basal half of the former projects freely beyond 

 in the form of a short and wide campanulate tube (figs. 5, 7, 8, ui). The basal mouth 

 of the latter is the lowermost base of the entire nectophore. and is armed w T ith two pairs 

 of serrate teeth, the two teeth of the dorsal pair being larger than those of the ventral 

 pair (figs. 7, 8). 



Somatocyst (fig. 4, cs, ventral view ; figs. 5, 6, cs, lateral view). — The somatocyst or 

 the coryphal cavity is ovate or spindle-shaped, about half as long and broad as the 

 hydrcecium. It is placed at the apex of the latter, in the apical prolongation of its vertical 

 main axis, and is nearly filled with large polyhedral entoderm cells. Its dorsal wall is 

 in contact with the upper half of the ventral wall of the nectosac. Its apex bears a 

 vertical oleocyst, containing a large ovate oil-bubble, about one-third as long and broad 

 as the somatocyst. 



