72 



HYDKOZOA 



have no otocysts, but only ocelli (Ocellatce), or they have 

 otocysts (fig. 11) (ectodermal sacs), four, eight, or over a 

 hundred, not homologous with tentacles, and sometimes in 

 addition ocelli ( Yesiculatce). The radial enteric canals are 

 usually four or eight in number, but may be more numerous, 

 whilst the marginal tentacles of the disc are either few or 



a 



Fig. 45. Fig. 4(3. 



Fin. 45. Medusiform person (Sarsia), one of the Anthomedusce, detached from a 



hydroid colony of the family Cori/nitlie. I:, the long manubrium, bearing (as 



an exception) medusiform bu.ls; a. mouth. 

 FIG. 46. Medusiform person, nne of the Anthomediisfe, detached from a hydro.^ 



colony of Syncoryne. Ocelli are seen at the base of the tentacles, and also (as 



an exception) groups of medusiform buds. 



very numerous. The genital glands always are placed in 

 the course of the radial canals of the disc (not in the manu- 

 brium), and stand out as groups of wart-like processes on 

 the sub-umbrellar surface (fig. 43). Their mode of dis- 

 charge is uncertain. 



FIG. 47. View of the oral surface nf one of the Lrptomediitup (1,-,-nc pelliici<l,t, 

 Haeckel), to show the numerous tentacles and the otocysts. ge, genital glands; 

 M, mmmbrimn; ot, otocysts; re, the four radiating canals; V"f, the velum. 



The (:'rili//itiili/nxti'ii of Allman, Skr.notoka of Cams, and Campanu- 

 Inrirr of authors form a well-marked group of hydroids which, when 



according to Allman, gives rise to a i/m'n-likp medusa (Antlw- 

 inciliisa;), is the only recorded exception to this correspondence. 

 They4'i/Hori'rfand other medusa> of similar structure have not been 

 traced into connexion with any hydriform trophosome, but we are 

 Hot justified therefore in concluding that they develop directly from 

 the egg without hydriform phase. The chief point distinguishing 

 the LeptomediisiB as a lot from the Anthomcdtmrr is the development 

 nf the generative bodies in the radial canals. This position is simi- 

 lar to that occupied by the same organs in Trui'lmMfiliiMc and 

 Sci/phomcduscc. Allman, however, considers the genital glands of 

 the L/'/i/i'i/K-i/iiwr, not as mere glands like those of Aurclia or 

 I'/mri/M.cca, but, as a series of buds a generation of aborted 

 ine.lusM- or sporosacs. In consequence he terms the medusa of the 

 LeptomediiscEa.'bla.aioeh.eme (or bud-producer), as distinguished from 

 a gonocheme (or genital-producer). In support of this view, 



AJlmaii (Monograph, 1874) adduces the various remarkable cases 

 of production of buds by medusge which have been recorded (fig. 

 44, 45, 46), and, further, the very striking similarity between the 

 structure of a lobe of the genital gland of Obelia and a sporosac 

 such as we find in Hydractinia. It seems necessary to accept 

 Allman's view on this matter, unless we are prepared to abandon 

 the homology of sporosacs with medusae in the case of hydriform 

 persons. 



The colonies of hydriform persons of the present group differ inter 

 sc according to the arrangement of the cups or hydrothecas. In 

 Phnnularidce they are sessile, and all on one side of a branch ; in 

 K-i-liihtridcB they are sessile, and alternately placed on either side ; in 

 Cam/panularidcK each cup is raised on a pedicel or stalk. The 

 medusiform persons sometimes remain abortive and sessile in their 

 gonangia. 



- h 



FIG. 48. Cai-j}iarin{i(Geryonia)lnist<jta,oneoftheTracliomedu5(?. (After Haeckel.) 

 a, nerve-ring; a', radial nerve ; 6, tcntaculocyst ; r, circular canal ; ^radiating 

 canal; g", ovary ; ft, pen.nia or cartilaginous process ascending from the carti- 

 laginous margin of the disc centripetally in the outer surface of the jelly-like 

 disc; six of these are perradial, six interradial. coi responding to the twelve solid 

 larval tenhicles, resembling those of Ciiniim; k\ dilatation (stomach) of the 

 manubrium; /, jelly of tlie disc; p, manubrium; /, tentacle (hollow and 

 tertiary, 2.e., preceded by six perradial and six interradial solid larval tentacles) ; 

 , cartilaginous margin of the disc covered by tliread-cells ; r, velum. 



Order 3. Trqckomedusce, Ilydromedtiftz which have as 

 sense-organs tentaculocysts. The otoliths (fig. 12) are 



FIG. 49. Diagram of a vertical section of Cui-intiiiita hnstttta, passing on the, 

 right through the whole length of a radiating canal, and on the left through 

 the outspread lobe of an ovary. I, gelatinous substance of the disc and gjtstric 

 stalk (manubrium); r, radiating canal; rs, its outer, rl, its inner wall; g, 

 ovaries; A% stomach (dilatation of the manubrium); Z, tonglie-like process of 

 the gelatinous substance; /(, cartilaginous piocess ascendingfrom the marginal 

 ring at the sile of a tentaculocyst ; c, circular canal; ft, tentaculocyst; r, 

 velum; , carlilaginous marginal ling. (From Gegenbaur.) 



formed by endodermic cells as in Sct/p/iomedtisce, and 

 ocelli may or may not be present on the tentaculocyst. 



