REPORT ON THE SIPHONOPHORiE. 



347 



and the cormidia monoclinic ; each ultimate branch of the clustered gonodendra is 

 monostylic, since it bears upon the same stalk a single female (f) and numerous male 

 gonophores (h), intermingled with some gonopalpons (q). The structure of these single 

 persons is the same as in the other Cystonectse (compare above, p. 313). The number 

 of gonodendra is usually four to six in the smaller, eight to twelve or more in the larger 

 species ; they are very richly branched, and arise from a common stalk with the siphons 

 and palpons (fig. 6). In the largest species each gonodendron bears some thousands of 

 gonophores. (Compare Huxley, 9, p. 105, pi. x. figs. 14, 15, and Chun, 86, p. 1168.) 

 The club-shaped androphores (PL XXVI. fig. 8, h) come to sexual maturity whilst sessile 

 on the stem, whilst the larger medusiform gynophores (fig. 8,/) become detached and 

 produce ova as free-swimming Anthomedusse. 



I. Subfamily Arethusice. 



Pneumatophore simple, without polythala 

 mous dorsal crest. 



II. Subfamily Caravellice. 



Synojms of the Genera of Physalidse. 



A single large main tentacle, 

 Several large main tentacles, 



Pneumatophore provided with a dorsal crest, 

 which is divided into a series of chambers 

 by transverse septa. 



A single large main tentacle, 

 Several large main tentacles, 



74a. Alophota. 

 lib. Arethusa. 



75a. Physalia 

 15b. Caravella 



Genus 74a. Alophota, 1 Brandt, 1835. 

 Alophota, Bdt., Prodromus, &c, 25, p. 37. 



Definition. — Physalidas with a simple vesicular pneumatophore, without dorsa. 

 polythalamous crest. Siphosome with a single large main tentacle. 



The genus Alophota and the following Arethusa compose together the subfarnily 

 Arethusidae, differing from the following subfamily Caravellidee in the absence of the 

 peculiar polythalamous dorsal crest of the pneumatophore. This characteristic crest is 

 also wanting in the young larvse of the large-sized Caravellidse ; the small Arethusidae, 

 therefore, may be regarded as the ancestors of the former, or also as young Caravel- 

 lidse, which have reached sexual maturity in the larval form (Psedogenesis). In every 

 case a crestless genus of Arethusidae must have preceded in older times the crested 

 Caravellidse, much in the same way as the crestless Rataria has preceded the crested 

 Velella. The crest of the pneumatophore, as an adaptation subservient to sailing, is a 

 secondary acquisition of later times. 



The genus Alophota was established by Brandt (25, p. 37) for a small crestless 

 Physalid from the Tropical Atlantic. Comparing the good figure which Mertens has left 



1 A lophota = Without crest, ct\6cpnx. 



