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



Between the former and the latter pair of ridges there arise in the basal third of the 

 exumbrella two convergent incomplete medio-lateral ridges, which end in the two large 

 ventro-lateral teeth of the nectosac mouth (n 3 , n 4 ). The five teeth of the mouth and 

 the basal parts of the ridges are elegantly denticulate. 



Nectosac (figs. 1-3, w). — The umbrellar cavity of the first nectophore is nearly 

 cylindrical, conical above, and in the contracted state four to six times as long as broad. 

 It occupies two-thirds of the length of the umbrella, and is placed in its dorsal half, close 

 to the ventral hydrcecium. From the top of the nectosac arises a long tubular csecum, 

 or a vertical apical canal (figs. 1, 2, cp) ; its blind end nearly reaches the outmost apex 

 of the umbrella. The nectocalycine duct (or the peduncular canal of the first nectophore) 

 descends from the top of the trunk obliquely towards the ventral side of the nectosac and 

 enters into it at a point between the first and second third of its height. It divides here 

 into the four radial canals of the nectosac. The shortest of these is the straight ventral, 

 the longest is the loop-shaped dorsal canal. The two lateral canals are shorter than the 

 latter, longer than the former, ascend like the dorsal, and then descend beyond the apex. 



Mouth of the Nectosac (fig. 1, lateral view; figs. 3 and 7, dorsal view; figs. 6 and 8, 

 basal view). The basal opening of the subumbrella is rather narrow, with a broad velum 

 (v), and protected by five convergent teeth, the ends of tbe above-mentioned longitudinal 

 ridges. The odd dorsal tooth (nd) and the two dorso-lateral teeth (n 1 , n~) are of nearly 

 equal size, half as large as the two ventro-lateral teeth (n 3 , n 4 ). 



Hydrcecium (fig. 1, id, lateral view ; fig. 2, ui, ventral view). — The funnel-cavity of 

 the first nectophore, or the hydrcecium, occupies the basal half of its ventral side. It is 

 slenderly campanulate and two-thirds as long as the nectosac, which is placed closely at 

 its dorsal side. The ventral half of the hydrcecium includes the peduncle or the apical 

 apophysis of the second nectophore (np), the dorsal half the upper part of the siphosome. 

 The basal mouth of the hydrcecium (fig. 8) is rectangular, three times as long as broad, 

 and armed with four pointed teeth, two ventral (n 5 , n 6 ), and two dorsal (n s , n*) ; the 

 latter are the ventro-lateral teeth of the nectosac-mouth. 



Somatocyst (figs. 1, 2, cs). — The acrocyst or the coryphal cavity of the first necto- 

 phore is a spindle-shaped or subcylindrical csecal canal, half as long as the hydrcecium. 

 It arises vertically from the top of the latter and extends over the top of the nectosac, 

 about as far as the basal half of its apical caecum. 



Basal Nectophore (figs. 1 and 4 seen from its right side, figs. 3 and 5 from the 

 ventral side). — The second, inferior, posterior or distal nectocalyx, is of the same length 

 as the apical nectophore, but not so broad. The form of its dorsal half (with the nectosac 

 and the quinque-dentate ostium) is very similar to that of the former ; but it has no 

 somatocyst, and the form of the ventral half and the apex are very different. The apical 

 part, above the nectosac, is nearly as long as the latter, isosceles triangular, and 

 elongated into a pointed apophysis, which is completely received within the hydrcecium 



