268 PHYSOPHORAE. 



have avoided this difficulty b\- using the older name Angelidae of Fewkes. 

 But Angela, the genus from which "Angelidae" is derived, belongs to a different 

 family, the Anthophysidae (p. 301). This fact invalidates Angelidae, and to 

 replace it Rhodaliidae Haeckel ('88a, p. 43, '88b), based on Rhodalia Haeckel 

 may be revived. 



Two other families of Physophorae, both monogastric, were described bj' 

 Haeckel ('88b), i. e., Circaliidae and Athoriidae. The only representative of the 

 latter which has been sufficiently described, Aihoria larvalis, was undoubtedly 

 a larval stagp, probably belonging to some Agalmid. Circalia stephanoma the 

 type of the Circaliidae, though retained by Chun in his list of Atlantic Siphono- 

 phores ('97b, p. 104), is also probably a young stage: indeed the mere fact that 

 it is monogastric is almost proof that such is the case, for no other Siphonophore 

 is known to retain the primitive monogastric condition permanently. Circalia 

 has been associated provisionally by Schneider and by Vanhoffen (:06, p. 34) 

 with the Rhodahidae, as the young of Stephalia, but whether it actually belongs 

 there can only be settled on fresh material. 



The phylogenetic relationships between the various families of Physophorae 

 form an inviting field for speculation; and especially is this true of the resem- 

 blance between Athorybia and the '"Athorybia" larvae of various Agalmidae. 

 It is easy to summarize the known facts in a few lines. Some Agalmidae, and 

 probably all, according to the recent studies of Woltereck (:05a, :05b), pass 

 through a complex larval stage, the "Athorybia" stage. This larva assumes 

 the adult structure as the result of a metamorphosis in which the primitive bracts 

 are lost. Now, Athorybia resembles this larva to an extraordinary degree. 

 It is true that we do not yet know whether the bracts of Athorybia are the 

 primitive ones permanently retained; but the development of the individual 

 bracts of the neighboring genus Anthophysa is so typical, and so different from 

 the early stages of nectophores as the latter are known in other Physophorids, 

 that it shows they are true bracts, not degenerate nectophores as some authors 

 have suggested. 



Chun's ('97b) discovery of rudimentary nectophores in Athorybia makes 

 the resemblance between it and that stage of the "Athorybia" larva just previous 

 to the dropping of the primitive bracts, when the buds for the future nectophores 

 are first visible, especially significant.. On the other hand the pneumatophore 

 of Athorybia is more highly specialized in its internal structure, particularly in 

 the great number of septa, than that of any Agalmid. 



The specialization of the pneumatophore and of the bracts, and the oblitera- 



