HYDROZOA 



75 



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

 1874). 



Relationship of the Ctenophora to the Hydrozoa. The 

 remarkable medusa-form recently described by Haeckel 

 (Sitzungtber. Jenaifche 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 Cydippe (Pletiro- 



FIG 57 Floating colonies of Siphoxophom. A, Diph 



B, A 



group of appendages from the tm of the same Diphfa.' C, Pkftapliora 

 hydrottatica. D, Separate nectocalyi of the same. , Cluster of female 

 iporosacs (aborted medusae 1 of Agalma tartii. a, stem or axis of the colony; 

 tf, pnenmatocyst (air-bladder); m, nectocalyx; c. sub-urn brellar cavity of 

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

 formed by the margin of the umbrella; /, hydrophyllhi in B. dactylozooids in 

 C; n. stomach; t, tentacles; g, sporosacs, (From Geeenbanr.) 



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 

 sub-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 Ctemaria Cte*ophora (Haeckel), one of the Anlhomfduia-. connecting 

 that croup with the Ctnophora. A. lateral view of the entire medusa ; B, two 

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

 sphere, that to the right a section passing nearly equatorial!}-, a. the eight 

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

 eight ctenophoral zones of PltvrobraeMa; 6, jelly of the umbrella; c, circular 

 muscle of the sub-umbrella ; <f. longitudinal muscles of the sub-nmbrella; t, 

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

 four perradial generative glands in the stomach wall (mannbrium); h. the 

 four perradial primary radiating canals; '. the eight adradial bifurcations of 

 the preceding : t. ring canal in the margin of the umbrella ; /. velum ; m, the 

 two Literal tentacle pooches ; n. the two lateral unilaterally fringed tentacles ; 

 o, the apical cavity (infnndibulum) above the stomach. The canal aialiM. 

 with its four primary and eight secondary rami agrees in Clnaria and Ptnro- 

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

 umbrella of the former. The mouth of Ctt*a:-ia is homologous with the 

 junction of the so-called funnel of Pltttretrathia 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 Ctexophora is paralleled .by 

 the stalk canal of medusa 1 , whilst the agreement between the tentacles anil 

 their pouches in Cttnaria and Ptewbraclria it 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 

 Hydromedusce and Ctenophora are such as to commend 

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



