SYSTEMATIC AND BIOLOGICAL ACCOUNT 85 



structure of these tentilla, but in the young tentillum the larger cap of the elongate nematocysts is 

 narrower and one-sided, and it only secondarily acquires its final hemispherical shape. The smaller 

 cap in its final form is provided with prominent cnidocils. In younger stages it is generally turned 

 to one side. The tentilla of Nectopyramis thetis are totally different. There the main battery of nemato- 

 cysts is confined to one side, and there is a long spirally coiled terminal filament. In N. diomedeae 

 there are a number of irregular surface ridges which are shown on PL V, figs. 2 and 3. 



C.po? 



= Cpa' 



Text-fig. 39. Nectopyramis diomedeae. A, the branching somatocyst-complex in the region of the hydroecium of the polygastric 

 stage. Specimen taken by Wm Beebe at Bermuda; B, the same, after Bigelow (191 lb, pi. 1, fig. 4) taken in Eastern Tropical 

 Pacific; C, a tentillum. 



Eudoxid. The 'central organ' is well figured by Bigelow (19116; pi. 1, figs. 5 and 6). In fig. 6 

 it can be seen quite clearly that the pedicular canal of the large nectophore arises from the central organ 

 and not from the nematocyst canal system, which is a closed system in the full-grown eudoxids of 

 Prayids. What cannot be seen so clearly in Bigelow's figures is that there is a semicircular bracteal 

 canal as in Rosacea ; that the hydroecial canal diverges from it at about the point marked in Bigelow's 

 fig. 6 with a 'pointer' labelled C.br. ; and that in some specimens at least the ascending canal lies on 

 the wall of the hydroecium for a short distance before passing to the apex. Its point of origin from 

 the semicircular canal is not directly opposite that of the ascending canal, which does not arise from 

 the central organ. As usual in Prayids, the central organ is closely attached to the semicircular canal, 

 and the fact that their lumina are quite separate is not easy to determine. This description will show 

 at once that the bracteal canal system of N. diomedeae can be homologized with that of N. thetis and 

 of Rosacea spp. In Nectopyramis diomedeae there are no lateral canals at the junction of the semi- 

 circular and hydroecial canals. 



