SYSTEMATIC AND BIOLOGICAL ACCOUNT 77 



end of the pedicular canal of the nectosac. In the definitive nectophore the pallial canal extends for 

 some distance beyond this point, and is usually called the descending branch of the somatocyst. One 

 is tempted to speculate as to why such large nectophores as those of Rosacea spp. appear to need no 

 somatocyst of the type found in other Calycophorae. The somatocyst of Hippopodiids is of an inter- 

 mediate type. The branched somatocyst of species of Praya and Stephanophyes seem to fulfil a circu- 

 latory rather than a flotational function, such as it is presumed to fulfil in other Calycophorae. 



Garstang (1946) made the interesting suggestion that in Calycophorae the aboral end of the larva 

 is aborted, and that for this reason Calycophorae do not develop the pneumatophore which he assumes 

 that their ancestors possessed. But Metchnikoff 's account of 9- and 10-day old larvae of Hippo- 

 podius hippopus, raised by himself at Villefranche eighty years ago, seems to show that it is from the 

 aboral end of the larva that its united bract and nectophore develops, although the nectosac itself lies 

 to one side. 



It appears to be a matter of some importance to observe the early stages of development of either 

 H. hippopus or Rosacea cymbiformis, both common Mediterranean species, so that the account of larval 

 development can be completed. 



In the spring of 1950 I made attempts at Villefranche to rear larvae of Hippopodius hippopus, but 

 specimens were scarce during my short visit, and although I kept the actively swimming and apparently 

 ripe female gonophore alive for ten days, and introduced active sperms to the eggs, I was unable to 

 induce the gonophores to shed their eggs and obtained no larvae. Chun (18880) reported that he, too, 

 had tried in vain. Metchnikoff himself reported that he had great difficulty in getting the species 

 to breed. My experiments were carried out in an improved Harvey ' rocker ', consisting of a battery 

 of sixteen 500 ml. beakers, in which plates of glass were kept rocking by a siphon-emptying water-can 

 and counter weight. The air temperature of the sous sol of the Station Zoologique in which the rocker 

 was installed was about 21 ° C, and subdued daylight entered from a small north window. The 

 gonophores appear to be heavy, and no doubt sink to some depth in the sea, where the temperature 

 would be lower. 



PRAYIDAE 



Nectopyramis Bigelow, 191 1 

 Type species N. thetis 

 The two ' deep-sea species described forty years ago under this generic name, N. thetis Bigelow 

 (1911a) and N. diomedeae Bigelow (191 ib) differ in several respects that are of some importance. 

 First, the dorsal and ventral radial canals of the nectosac of N. thetis do not arise in common with the 

 lateral pair, but are far separated. In this N. thetis agrees with Archisoma natans. Secondly, the 

 eudoxid of Nectopyramis thetis resembles that of Archisoma natans and differs from that of Nectopyramis 

 diomedeae in having a special swimming bell with similarly dissociated canals. Thirdly, N. thetis, 

 unlike N. diomedeae, but like Archisoma natans (which, of the Nectopyramidinae, has the most simple 

 somatocyst (canal system), consisting of one longitudinal canal), has an open hydroecial cavity 

 extending the whole length of the polygastric stage of the animal. There is also a sharp bend in the 

 middle region of Nectopyramis thetis and Archisoma natans near the base of the stem, as in Rosacea 

 plicata and R. cymbiformis. In these three ways it would seem that Nectopyramis thetis and Archisoma 

 natans are more closely related than the two so-called species of Nectopyramis are to each other. 

 Bigelow & Sears (1937) accepted my suggestion that Nectopyramis is a Prayid genus, and gave some 

 more excellent figures of the type species N. thetis. It would be best perhaps to include Archisoma 



Bigelow (1919) mentions a name N. albatrossi. I have failed to find it elsewhere, and it appears to be a nomen nudum, 

 possibly the manuscript name he used for N. diomedeae before publication of his 'Albatross' Report. 



