HYDROZOA 



and Jenaische ^eitsch., vol. viii. 



75 



Zool., vols. XV., xix., 

 1874). 



Belationship of the Ctenophora to the Hydrozoa. — The 

 remarkable medusa-form recently described by Haeckel 

 (Sitzungsber. Jenaische Gesellseh., 1878) as Ctenaria cteno- 

 phora, and classed by him amongst the Anthomedusce, seems 

 to furnish a very direct transition from the structure of a 

 medusa to that of such a ctenophor as Gydippe {Pleuro- 



FfG 67.— Floating colonics of Siphonophora. A, Diphyes campanulala. B, A 

 group of appendages from t!ie stem of the same Diphyes. C, Fhysophora 

 hydrostatica. D, Separate nectocalyx of the same. E, Cluster of female 

 sporosaca (aborted medusse) of Agalma sarsii. a, stem or axis of the colony; 

 a', pneumatocyst (air-bladder) j m, nectocalyx ; c, sub-umbrellar cavity of 

 nectocalyx ; «, radiating canals of the umbrella of the nectocalyx : o, orifice 

 formed by the margin of the umbrella ; t, hydrophyllia in B, dactylozooids in 

 C; n, stomach; t, tentacles; gr, sporosacs. (From Gegenbanr.) 



brachia). The woodcut and appended explanation (fig. 58) 

 copied from Haeckel's memoir will render the relations 

 of the two forms clear. Ctenaria has the margin of its 



disc narrowed so as to give the organism a spherical form. 

 The approximated margins bound an orifice leading to the 

 Biib-umbrella space. This orifice corresponds to the so- 

 called mouth of a Cydippe. Further, Ctenaria has two, 

 and only two, long-fringed tentacles, like those of Cydippe, 

 and each springing from a pocket as in that genus, and 

 on the surface of its spheroidal umbrella eight rows of 

 differentiated ectodermal cells, which though not ciliated 



Fio. 58. — Ctenaria Ctenophora (Haeckel), one of the AnthoTnedusce, connecting 

 that group with the Ctenophora. A, lateral view of the entire medusa ; B, two 

 horizontal views, that to the left representing the surface of tlie aboral hemi- 

 sphere, that to the right a section passing nearly equatorially. a, the eight 

 (ciliated?) rows of thread-cells, adradial in position, and con*esponding to the 

 eight ctenophora! zones of Pleurbbi^achia; &, jelly of the umbrella; c, circular 

 muscle of tlic sub-umbrella ; (f, longitudinal muscles of the sub-umbrella; e, 

 stomachal dilatation of the enteric cavity ; /, the sixteen oral tentacles ; gr, the 

 foQr perradial generative glands in tile stomach wall (manubrium); h, the 

 four peiTadial primary radiating canals ; i, the eight adradial bifurcations of 

 tlie preceding ; ft, ring canal in the margin of the umbrella; 7, velum ; m, the 

 two lateral tentacle pouches ; w, the two lateral unilaterally fringed tentacles ; 

 0, the apical cavity (infundibulum) above the stomach. The canal system, 

 witli its four primary and eight secondary rami agrees in Ctenaria and Pleuro- 

 brachia. The mouth of the latter is homologous with the mai'gin of tho 

 umbrella of the former. The mouth of Ctenaria is homologous with the 

 junction of the so-called funnel ,of Fleurobrachia with its so-called digestive 

 cavity. This last is the homologue of the sub-umbrellar cavity of Ctenaria. 

 The apical opening or openings of the funnel of Ctenophora is paralleled .by 

 the stalk canal of medusse, whilst the agreement between the tentacles anil 

 their pouches in Ctenaria'axii Pleurobrachia is complete. 



correspond closely in position with the eight ctenophoral 

 ambulacra of Gydippe. The disposition of the enteric canal- 

 system of Ctenaria is, as shown in the cut, also transitional 

 in the direction of Cydippe. Apart from the existence of 

 Ctenaria, the homologies suggested by Haeckel between 

 Hydromedusoi and Ctenophora are such as to commend 

 themselves very stronglv to acceptance (e. k. l.) 



