24 DISCOVERY REPORTS 



The calycophoran condition is best seen in the Prayids and in the Hippopodiids. Here the budding 

 zones arise and remain close to each other, and the increase in length of nectosome and siphosome 

 takes place in opposite directions. This is particularly noticeable in Hippopodiids, where the region 

 adjoining the joint budding zones forms an upper, progressively twisting loop, and the nectosome 

 forms a spiral-shaped, pendant housing (hydroecium) for the siphosome, which hangs down inside 

 and is retractable within it. In the early stages of Hippopodiid growth the larval nectophore is 

 attached above the joint growing-zone, but is later cast off. 



Bz.Gz.-_ 



Text-fig. 5. A, larva of Physalia physalis (after Okada, 1932) for comparison with B, larva of Nanomia bijuga, C, young 

 Physophora hydrostatica (diagrammatic) after elongation of nectosome, and D, adult Athorybia rosacea (diagrammatic), 

 E, diagrammatic ventral view of D to show the succession of gastrozooids. In all four species there is a terminal protosiphon 

 Gz 1 , one or more secondary gastrozooids in a nearby group and a separate budding zone Bz.Gz. for the main succession of 

 gastrozooids. 



Leaving out of account the larval Hippopodiid nectophore, which is specialized precociously to 

 support the bud-colony, it would be possible theoretically to derive the Hippopodiid condition from 

 that of the long-stemmed Physonect by imagining that with the disappearance of the pneumatophore, 

 the pedicel or foot-stalk of the first nectophore grew continuously in length like that of the protosiphon 

 (first gastrozooid), and that each successive nectophore was budded from the foot-stalk of the one 

 before. Thus the nectosomal budding zone would remain near the siphosomal one, instead of being 

 carried upwards further and further away from it as it is in Physonectae. In this way the lengthening 

 of nectosome and siphosome in Calycophorae would take place in opposite directions instead of in the 

 same one (cf. frontispiece). 



In both Prayids and Diphyids the definitive nectophores are reduced to a number which varies 

 between four and one, but the arrangement of budding zones is difficult to see because it is not easy 

 to anaesthetize the stem in that region, so that details are obscured by overcrowded buds. 



PHYSONECTAE: PRIMITIVE OR DERIVATIVE 

 Once having been evolved, it is evident that the nectophores of Calycophorae and Physonectae are 

 homologous structures, although the situation in Calycophorae is complicated by what Garstang 

 supposes to be the addition of a bract, now represented by the somatocyst. The relationship of the 

 budding zone of the nectophores with that of the siphosome in the two groups was discussed above. 

 We now have to decide which group, Physonectae or Calycophorae, is primitive and which derivative. 

 Garstang published the view which I myself have always held, namely, that the Physonect ancestors 

 appeared first. In text-books the order in which the groups are dealt with implies that they appeared 

 last. As Garstang said, it is the Calycophore which has undergone the most radical change, and it may 





