13 8 . DISCOVERY REPORTS 



are commonly opaque. At Villefranche I have observed that the nectophores of undisturbed specimens 

 of H. hippopus are quite transparent, but that when disturbed they immediately become opaque. 

 After a rest they once more become transparent. As far as is known no research has been carried out 

 upon this phenomenon. But I have recently found a description of this same phenomenon by Chun 

 (1888 a) which he observed whilst working in the Canaries. He said that the turbidity occurred in 

 the ectoderm of Hippopodius, and added that a related phenomenon observed in the eudoxid of 

 a Ceratocymba was due to the appearance of extremely fine granules in the neighbourhood of the 

 horn-like canals of the somatocyst. These granules later spread throughout the mesogloea, but 

 disappeared again in about half an hour if the eudoxid was left in repose. 



In 'Discovery' hauls so far examined I have seen eleven 'spotted' anterior nectophores. Neither 

 the number, size, degree of opacity nor symmetry of their opaque spots is constant, if my identifica- 

 tions of these small and ill-preserved nectophores are correct. 



In the better preserved of these nectophores of Heteropyramis maadata examined, nine opaque 

 spots can usually be seen, one each at the apex and basal end of each dorso-lateral ridge, and three 

 intermediate ones on each of these ridges. I have observed as few as eight spots and as many as 

 sixteen in all. 



In the following diagram the kind of variation that exists in the opaque spotting is shown. 



ise? 



1567 



2636 264B IOOC 26 46 693 



Text-fig. 70. Heteropyramis maadata. Diagram of distribution of pigment-spots 



in specimens from various 'Discovery' Stations. 



A serious doubt has arisen in my mind as to whether H. maadata and Thalassophyes crystallina 1 

 are not really one and the same species. The difficulty is that the spotted form Heteropyramis maadata 

 is rare, and the twelve nectophores that I have examined were none of them sufficiently well preserved 

 to enable me to construct a very reliable drawing of the side-view. Moser, who described the necto- 

 phores as flattened dorso-ventrally did not attempt to draw such a lateral view. Consequently, it is 

 difficult to compare her published figures of the nectophores of the two forms. The ventral facets are 

 similar, and both have two small incomplete ventro-lateral ridges, one on each side of the opening 

 of the hydroecium. I can see no significant external differences in shape or size. As to the somatocyst, 

 the absence of opaque spots — in Thalassophyes — on the lateral ridges does seem to be associated with 

 a large, well-preserved and vacuolated somatocyst, the proximal part of which lies obliquely to the 

 main axis of the nectophore; the distal part, which is a fine tube, lies roughly at right-angles to the 

 proximal part. In one or two of the spotted forms the somatocyst can be partially seen. It appears 

 to be thin-walled, never well preserved and straighter. Perhaps the terminal part of the somatocyst 

 of spotted forms approaches more nearly to the apex of the nectophore. Two nectophores from 

 'Discovery' Station 2636 have somatocysts of this second type, but no opaque spots other than small, 

 faintly discernible opaque areas at the apex of each. It may possibly be found in future that opaque 

 spots can be present or absent in nectophores of Heteropyramis maadata. In this connexion my 

 observations on the temporary opacity of the nectophores of Hippopodius hippopus should be borne 

 in mind. It seems to be all the more probable that in the nectophores, opaque spots may be present 



1 Text-fig. 72. 



