22 DISCOVERY REPORTS 



as the first diagram (Text-fig. i) shows. But there are to be found in the plankton very young stages 

 of the anterior nectophore of Abylines and Abylopsines with a single gastrozooid, which suggests 

 that they are larvae. I have accordingly arrived at the tentative conclusion that the anterior nectophore 

 of Abylids is the persistent larval nectophore, and that the anterior nectophore of Bassia represents 

 an initial rather than a late stage in evolution. It may be compared in the second diagram (Text-fig. 2) 

 with larval nectophores of other Calycophorae, and with the nectophore of Sphaeronectes. I have bred 

 one species of Sphaeronectes at Villefranche, and it is evident that the adult nectophore is the persistent 

 larval one. It is interesting then, to see that although, as Garstang pointed out, the pioneers and the 

 writer of one modern text-book, Moser, misconstrued the structure of Sphaeronectes as representing 

 a medusa with an exumbral manubrium, they were not far wrong in thinking it was the nearest 

 approach to an archetype of the Siphonophora, since the adult is at any rate most like what we imagine 

 the ancestor of the Calycophorae to have been. Perhaps it is a neotenous form, like Nectopyramis 

 diomedeae. 



BUDDING ZONES 

 It is evident from a fresh study of living and preserved post-larvae that in such forms as Nanomia bijuga, 

 Agalma okenii (Text-fig. 27), and to some extent also in Physophora hydrostatica, the budding zones for 

 the nectosome and for the siphosome, where true gonophores are now budded, arise on opposite sides of 

 the larval air-sac (Text-figs. 3-5), although the significance of this is not yet understood. 1 In the adult 

 of Forskalia edwardsii the nectophores, siphons (gastrozooids) and gonophores appear all to be budded 

 from the ventral side, as far as I have been able to ascertain. But even in an anaesthetized Forskalia 

 there is so much crowding together of the siphosomal buds that it makes observation very difficult. 

 In many Physonects whose siphosomal budding zone I have examined, there are indications that the 

 successive gastrozooid-buds arise in a curved line that lies obliquely to the main axis or stem 

 (Text-fig. 4) as in the nascent lobe of Physophora hydrostatica and in Athorybia rosacea (Text-fig. 5). 

 Further work is needed on this point, for in both species of Rhizophysa, a contracted specimen shows 

 that, though the budding zone of cormidia has always been thought to be single and ventral, it is only 

 very close to the start of the budding zone that this can be seen to be true. As successive gastrozooids 

 move distad they shift alternately to the right and left sides, leaving the gonophores between in the 

 mid-ventral meridian. It is only further down the stem that they secondarily appear to arrange 

 themselves in a single meridian again. 



Although, as I shall show below, it is possible theoretically to derive the calycophoran budding 

 arrangement from that of the Physonectae, no one, as far as I am aware, has drawn attention to the 

 true nature of these budding arrangements and to the striking difference between the relationships 

 of siphosome to nectosome in the two groups. 



In a mature, long-stemmed Physonect such as Nanomia (Stephanomia) bijuga and Stephanomia 

 rubra (originally known as Agalma rubra Vogt), the youngest proximal part of the siphosome is 

 distal to the oldest part of the nectosome, so that the two parts of the stem must have increased in 

 length in the same direction ; and the budding zone of the siphosome must have been carried distad 

 (in an oral direction) in the course of growth from the larval stage, with the result that nectosome and 

 siphosome form a single pendant stem, and the nectosome separates the two budding zones. 2 Garstang's 

 description of the arrangement (1946, pp. 106, 147) is misleading and gives the impression that the two 

 budding zones lie close together between nectosome and siphosome in Physonectae — a statement 

 which is true of Calycophorae but not of Physonectae. 



1 Metchnikoff (1874) figured the two budding zones on opposite sides of the stem in the larvae of Sulculeolaria quadrivalvis 

 (' Epibulia aurantiaca'), pi. 7, figs. 12-14, an ^ in the post-larva of Agalma elegans ('A. sarsii'), pi. XI, fig. 2. Chun (1897a, 

 fig. 6c) figured the two zones in a larva of Hippopodius hippopus. 2 See frontispiece. 





