GONODENDRA 347 



In my completely fresh study of Physalia, the task of finding out how the gonodendra were con- 

 structed and developed was started in an exploratory way by examining the oldest and youngest stages 

 that could be found. At Arrecife, I collected as many as possible of the large gonodendra dropped 

 by live specimens in the laboratory tanks. Scars are often seen in places were there should be, but is 

 not, a gonodendron (Text-fig. 17) : this suggests that the dropping of a gonodendron occurs naturally. 

 I soon found that the egg-shaped gonophores, hitherto supposed to be all male, were in any single 

 gonodendron either all male or all female, and that the stalked medusoids, generally supposed to be 

 female gonophores, were asexual nectophores and not gonophores at all, thus confirming Steche's 



view (1907). 



Microscopical preparations were made of the young stages of the terminal branchlets of the genital 

 clusters (which Schneider called 'Genitaltrauben'), and the growth-stages were seriated. Finally an 

 attempt was made to work back from the oldest stages and forward from the youngest to a meeting- 

 point which could be interpreted in terms of younger growth-stages and of mature structure. 



Every primary gastrozooid develops a gonodendron at its base,* and the whole complex— gastro- 

 zooid, tentacle and ampulla, and gonodendron— is referred to in this report as a tripartite 



group. 



A gonodendron develops when a main gastrozooid buds-off a number, varying from five to seven, 

 of gonozooids (secondary gastrozooids) budding from one another and lacking the characteristic type 

 of tentacle. The gonozooids bud from the base of a primary gastrozooid (PI. XIV, figs. 1, 2) and the 

 common base elongates to form a peduncle (Text-fig. 15), and the peduncles of the gonozooids 

 elongate to form branches of the gonodendron (Text-fig. 25). The whole structure, somewhat re- 

 sembling the wrist, palm and fingers of the hand, curls up as when the thumb and little finger are 

 opposed, and eventually forms the globular gonodendron shown in PI. XX, figs. 2, 6. The bases of the 

 gonozooids give rise to the genital clusters, consisting of successively smaller palpons, and of gonophores, 

 jelly-polyps, and nectophores (PI. XX, figs. 3, 4). The gonophores represent the original, now much 

 reduced, adult sexual phase of Physalia. The clusters branch and rebranch (Text-figs. 25, 26) and come 

 to form the ultimate branchlets of the gonodendra (PI. XX, fig. 5). At first they are short (PI. XX, fig. 3), 

 but they grow very much longer than the gonozooids, which finally appear to arise from the basal 

 branches of a mature gonodendron (PI. XVII, fig. 2). 



The largest of the gonodendra which I preserved, a female one, was a globular mass of palpons and 

 gonophores measuring 4 or 5 cm. in diameter (6 or 7 cm. when flattened in a dish), and consisted of 

 seven main branches radiating out from its stem. Each main branch rebranched at least five times, so 

 that there would be about 224 (7 x 2 5 ) terminal branchlets carrying 448 gonopalpons (two per branch- 

 let), 224 medusoid nectophores and 2400 gonophores (ten per branchlet). Very many gonodendra were 

 present in all but the very youngest stages of development, often five or more well-developed ones at 

 a time. The potential number of gonodendra (PI. XX, fig. 1) formed on the main zone of cormidia 

 alone, based on an analysis of cormidium II of specimen no. Lanzarote 2, is about 500, and the 

 number of gonophores, or adults, that they might bear would be at least a million. 



The muscular peduncle, or stem, and the branches of the gonodendra are highly contractile, but I 

 have not noticed much sign of movement of the nectophores and palpons. I think it probable that 

 whole gonodendra and perhaps later the terminal parts of the branchlets also become detached in the 

 sea. Generally five or six gonozooids, from the bases of which the genital clusters grow, are found at 

 the bases of the branches of these dropped gonodendra, but (as expected) never any tentacles. 



Analysis of the complexity of the gonodendra had been attempted in 1908 by Lens and van 



* Delage and Herouard (1901) show the gonodendron as arising from the pedicel of the ampulla— this is not correct. 



