EEPOET ON THE SIPHONOPHOR^E. 307 



Cystonectse. He united in 1882 the Rhizophysidse and Physalidse under the name 

 Pneurnatophoridse, and separated them from the Physophoridse (our Physonectse) (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 Rhizophysidaa 

 and Physalidse, 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 similar families Among the Physonectse. The monogastric 

 Cystalidse correspond to the simple Athoridse. Two polygastric families with a very 

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

 (with monogastric cormidia) are comparable to the Agalniidse, the Salacidse (with 

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

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

 similar to the Diseolabidse, and the Physalidse in some respects to the Anthophysidse ; 

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

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

 Physalidse from all other Siphonanthse. 



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

 and feeding portion, exhibit a very different relation in the various Cystonectse. 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 Cystalidse, and the polygastric 

 Cystonectse of the four other families ; it is composed in the Cystalidse (PL 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 Cystalidse 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 Brachystelinise (Epibulidse, PI. XXII. 

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

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

 Pis. XXIII., XXIV.; and Salacidse, PI. 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 Siphonophorse, 

 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, arid the opposite ventral the inferior side. 



