REPORT ON THE SIPHONOPHOR^E. 307 



Cystonectae. He united in 1882 the Rhizophysidae and Physalidae under the name 

 Pneumatophoridae, and separated them from the Physophoridae (our Physonectae) (86, 

 p. 1168). He pointed out as a common character the absence of nectophores and bracts, 

 and the peculiar structure of the gonodendra. Chun further published the first 

 accurate description of the peculiar structure of the pneumatophore in the Rhizophysidae 

 and Physalidae, and of the metamorphoses of the young Physalia (48, 83, pp. 529, 557, 

 574). 



The five different families of Cystonectse which are described in the sequel, exhibit 

 interesting relations to simflar families among the Physonectae. The monogastric 

 Cystalidae correspond to the simple Athoridas. Two polygastric families with a very 

 prolonged tubular trunk have analogous representatives in both orders ; the Rhizophysidae 

 (with monogastric cormidia) are comparable to the Agalmidse, the Salacidae (with 

 polygastric cormidia) to the Apolemidae. Two other polygastric families possess a 

 shortened and inflated vesicular trunk of the siphosome ; of these the Epibulidae are 

 similar to the Discolabidae, and the Physalidae in some respects to the Anthophysidae ; 

 the peculiar secondary development of the gigantic pneumatophore, however, and its 

 consequences for their further divergent organisation, remove still more widely the 

 Physalidae from all other Siphonanthae. 



Nectosome and Siphosome. — The two different main portions of the corm, swimming 

 and feeding portion, exhibit a very different relation in the various Cystonectae. The 

 nectosome, or the swimming body, is represented only by the large pneumatophore and 

 corresponds to the modified umbrella of the original medusome. The siphosome, on the 

 other hand, exhibits a different shape in the monogastric Cystalidae, and the polygastric 

 Cystonectae of the four other famdies ; it is composed in the Cystalidae (PI. XXII. figs. 

 1-5) of a single large siphon (the manubrium of the original medusome), and of various 

 organs budding from its base (a tentacle, a corona of palpons, and a gonodendron). The 

 single siphon of the Cystalidae corresponds to the axial trunk of the four other families ; 

 from its ventral side arise numerous cormidia by budding. These secondary cormidia, 

 composed of siphons, palpons, tentacles, and gonodendra, are sometimes ordinate, at other 

 times loose ; they are densely aggregated in the Brachysteliniae (Epibulidae, PI. XXII. 

 fig. 6; and Physalidae, PI. XXVI.), with a shortened and inflated vesicular stem ; they are 

 loosely scattered and separated by long internodes in the Macrosteliniae (Rhizophysidae, 

 Pis. XXIII., XXIV.; and Salacidae, PL XXV.), which possess a long tubular stem. 

 The nectosome and siphosome are usually separated by a constriction corresponding to 

 that portion of the original medusome on which the manubrium is inserted into the centre 

 of the subumbrella. Another structure, differing from that of all other Siphonophorae, 

 is exhibited by the peculiar Physalidae. The hypertrophic pneumatophore extends here 

 into the trunk of the siphosome, along its dorsal side, so that this side becomes the 

 superior, and the opposite ventral the inferior side. 



