346 DISCOVERY REPORTS 



(8) I have examined early stages of the gas-gland only in optical section and as seen through the 

 (cleared) pneumatocodon, so that I cannot add much to what Okada (1935, figs. 2 and 3) showed 

 of it. 



(9) It will be realized that because the oral half of the larva seems to be very muscular, the shape 

 of the specimens varies a good deal with the state of contraction and content of food. The extent of the 

 saccus too must vary with the content of gas at any particular time. 



Physalia is distinguished from almost every other siphonophore by this complexity of branching by 

 budding of the cormidia. Whereas in two sub-orders of siphonophores these cormidia bear bracts, and 

 in one of them the terminal cormidia break off to lead a free existence and perform the function of 

 reproduction, in the sub-order Cystonecta to which Physalia belongs there are no bracts and only the 

 gonodendra break off. The most striking feature of the budding-pattern that distinguishes Physalia 

 from its nearest allies, the cystonects Rhizophysa, Batkyphysa and Pterophysa, is that in them there is 

 a single linear axial arrangement of successive tripartite groups (Urgruppen), namely gastrozooid, 

 tentacle and gonodendron, the youngest group being nearest the float, whereas in Physalia each of the 

 original tripartite groups gives rise to a series of up to a dozen lateral groups of the same kind, while 

 still younger groups are budded from the bases of these. 



In spite of the great complexity of growth, and in spite of the fact that, owing to varying stages of 

 growth and states of contraction in the twenty young specimens from Lanzarote examined by me, no 

 two look exactly alike, I have seen nothing in specimens from all oceans to make me suspect that I 

 have been dealing with more than one species of Physalia. The view expressed by Steche (1910, 

 p. 361) that there is one pattern of budding-characteristic of a species utriculus and another of a 

 species physalis is not acceptable to me, particularly since Okada (1932) has demonstrated that the 

 supposed characteristics of a Pacific utriculus are those of a juvenile specimen of physalis. 



The only other siphonophore at all like Physalia is a remarkable specimen, now lost, taken by 

 H.M.S. 'Challenger' and described by Haeckel (1888) as Salacia polygastrica. It was later renamed 

 Salacella by Delage and Herouard (1901) because the name Salacia was preoccupied. Haeckel not 

 only named this delicate specimen — the stem measured only half a millimetre in diameter — which 

 was 'much contracted in the spirit bottle', but he softened 'it gradually with water to make it so 

 elastic that it could be extended to that degree which is figured in (his) plate xxv, fig. 1 '. Haeckel's 

 idealized figure shows a truly remarkable animal. No other specimen has ever been seen, but if such 

 animals do exist they have many features in common with Physalia, from which they differ strikingly 

 in the nature of their air-sac and by the fact that the cormidia are borne on a long stem. The existence 

 of Salacella, if confirmed, would demonstrate conclusively that Physalia retains characteristics of 

 larval forms such as are also found in physonect genera. 



There is one striking morphological feature of Physalia which remains a puzzle, namely the 

 arrangement of the cormidia in two zones, oral and main. It may be that one original complete series 

 has become interrupted for some functional reason connected with the dynamics of orientation to the 

 wind, but more probably precocious growth in some main cormidia left little space for the oral ones 

 and so led to retardation in growth and reduction in complexity. 



Structure and Development of the Gonodendra 



(Pis. XX-XXIII, Text-figs. 25-27) 



Whereas in the cystonects, Rhizophysa spp. and Pterophysa conifera, a single gonodendron is budded 

 out between neighbouring gastrozooids as a simple ovoid sac, which only subsequently develops 

 terminal side-branches, in Physalia the gonodendra are much more diffuse structures. 



