84 DISCOVERY REPORTS 



canal (C.ped.) of the nectosac and then continues distad along the face of the hydroecium. 

 Above, it leaves the hydroecial wall and continues (C.pa 2 ) towards the apex of the bract, giving off 

 four or more long, alternate lateral branches. At the point where C.pa 2 leaves the hydroecial wall the 

 longitudinal median canal forms on either side, as in N. thetis, a curved lateral canal, which runs on 

 the wall of the hydroecium. On the left side it forks, one complicated branch (Bigelow's C.h.l.) 

 running on the left wall of the hydroecium, and the other giving rise to C.pa 3 , which very shortly 

 after the fork gives off a downward branch (Bigelow's C.h.r.) on the right wall of the hydroecium. 



Returning again to the base of C.pa 2 , the longitudinal canal, on the right side of C.pa 2 , gives off 

 C.pa 1 , which almost at once gives off a descending branch, C.h.l. 2 , that runs on the left wall of the 

 hydroecium. 



The problem is how to homologize the canal systems of N. thetis and N. diomedeae. My tentative 

 solution is that the small C.h.l. 2 in N. diomedeae is the true left hydroecial canal, and that Bigelow's 

 C.h.l. is a secondarily developed canal. We should then see in both species a similar arrangement — 

 an ascending canal C.pa 2 , a right and left ' dorsal ' canal C.pa 3 , C.pa 2 , and a right and left hydroecial 

 canal C.h.r., C.h.l. 2 . In N. diomedeae the canal system is more complicated still, but the basic 

 arrangement is similar to that in N. thetis. 



The whole nectophore is twisted, so that the nectosac opens on one side instead of dorso-basally, 

 and the branches of the somatocyst have become secondarily displaced. Bigelow's (191 1 b) description 

 of the system, as far as the lower part and the free upper part of the longitudinal median canal is 

 concerned, agrees with mine. After this Bigelow (191 \b, p. 192) says, 'at the point at which it [the 

 ascending canal] bends apically it gives off a branch which runs over the left-hand face of the 

 hydroecium [his C.h.l. of fig. 4] and a short distance further on gives off a second trunk which passes 

 over its right-hand face [his C.h.r.]. These two canals of the hydroecium. . .'. In my view only one 

 of these, Bigelow's C.h.r., is the homologue of an hydroecial canal (the 'right' hand one) in N. thetis. 

 Bigelow did not figure or describe what I take to be the true, short, simple, left-hand hydroecial 

 C.h.l. 2 . The 'explanation' of Bigelow's (191 lb) plate 1 (which does not mention fig. 6, part of the 

 eudoxid) corrects certain lettering in figs. 3 and 4. It should be noted that the lettering C.pa 1 and 

 C.pa 2 also in these figures should be transposed. The 'descending branch', to which Bigelow refers 

 on p. 192, can be seen at the top on the right in his figs. 3 and 4, descending from C.ped. (marked on 

 the plate C.pa 3 ). With these trifling corrections made it will be more easy to enjoy Bigelow's descrip- 

 tion and figures, and to understand the homologies of this complex canal system, which he figures so 

 beautifully. To clarify my remarks, I give a new figure (39 A) of part of the canal system, and reproduce 

 a comparable one (39 B) by Bigelow. 



Since the adult nectophore of N. diomedeae retains in its nectosac the type of radial canals found in 

 larvae of other Prayinae (its own larva is unknown), and its hydroecium has the pocket-shape so 

 characteristic of larvae, it is reasonable to regard it as a neotenous form. Secondarily its somatocyst 

 has become very much complicated (see Text-fig. 39). 



The tentilla of N. diomedeae (Text-fig. 39C), though partly described by Bigelow (191 ib), have 

 never been figured. They are relatively large and of peculiar construction when mature, borne on 

 long, loosely coiled pedicels. The apical part consists not of a terminal filament but, as in the larval 

 tentillum of Physophora hydrostatica, of a small hollow cap of ovate nematocysts that appear to be 

 stenoteles. This cap is from 0-2 to 0-25 mm. in diameter, and is perched on the apex of a large hemi- 

 spherical cap of longer scimitar-shaped nematocysts. The larger cap measures from 0-35 to 0-4 mm. 

 in diameter. Into it penetrates a tapered endodermal core, round which, externally to the cap, is 

 twisted irregularly a long, double, structureless, elastic cord. Proximal to this cord is a thickened 

 opaque length of ectoderm. It is not possible at the moment to make a further examination of the 



