HYDROZOA 



75 



Zool., vols. xv., xix., and Jennische Zeitsch., vol. viii., 

 1874). 



Relationship of the Ctenophora to the HyJrosoa. The 

 remarkable medusa-form recently described by Haeckel 

 (Sitssungsber. Jenaische Gesel/sch., 1878) as Ctenaria ctena- 

 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 Cydippe (Pleuro- 



FIG 57. Floating colonies of Siphonophora. A, Diphyes campanulata B, A 

 group of appendages from the stem of the same Diphyes, C, Physopliora 

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

 sporosacs (aborted medusa?) of Agalina sarsii. a, stem or axis of the colony; 

 a', pneumatocyst (air-bladder); m, nectocalyx; c, sub-umbrcllar cavitv of 

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

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

 C; n, stomach; i, tentacles; g, sporosacs. (From Gegenhaur.) 



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 ns to give the organism a spherical form. 

 The approximated margins bound an orifice leading to the 

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

 called mouth of a Cydippe. Further, Ctnuu'iu has two, 

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

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

 on the surface of its spheroidal umbrella eight rows of 

 differentiated ectodermal cells, which though not ciliated 



FIG. 58. Ctenaria Ctenophora (Haeckel), one of the Antliomeduscp, connecting 

 thut group with the Ctt'iwphora. A, lateral view of the entire medusa ; B, two 

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

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

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

 eight ctenophoral zones of Plcurobracliia; {>, jelly of the umbrella; c, circular 

 muscle of the sub-umbrella ; rf, longitudinal muscles of the sub-umbrella; e, 

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

 four perradial generative glands in the stomneh wall (roannbrrnm) ; ft, the 

 four perradial primary radiating canals; ?, the eight adradial bifurcations of 

 the preceding; k, ring canal in the margin of the umbrella; /, velum; m, the 

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

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

 with its four primary and eight secondary rami agrees in Clcnaria and Plturo- 

 lirachia. The mouth of the latter is homologous with the margin of the 

 umbrella of the former. The mouth of Ct'iifnia is homologous with the 

 junction of the so-called funnel of l'l>'iir:>l'r<i<'liin with its so-called digestive 

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

 The apical opening or openings of the funnel of Cti'nopliora is paralleled .by 

 the stalk canal of medusffi, whilst thy agreement between the tentacles and 

 their pouches in Ctenaria and Plcurobrachia is complete, 



correspond closely in position with the eight ctenophoral 

 ambulacra of Cydippe. 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 

 IlydromeduscK. and Ctenophora are such as to commend 

 themselves very stronglv to acceptance (E. E. L.) 



