72 



HYDROZOA 



have no otooysts but only oceUi {Ocdlata,), or they have 

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

 hundred, not homologous with tentacles, and sometimes in 

 addition ocelli {Vesiculatoe). 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 



Allman {Monograph, 1874) adduces the various remarkable casea 

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

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

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

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

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

 the homology of sporosacs with medusae in the ease of hydriform 

 persons. 



The colonies of hydriform persons of the present group differ irOer 

 se according to the arrangement of the cups or hydrothecse. In 

 Plumularidce tliey are sessile, and all on one side of a branch ; in 

 Sertularidoe they are sessile , and alternately placed on either side ; in 

 Ccmtipanularidce each cup is raised on a pedicel or stalk. The 

 medusifoxm persons sometimes remain abortive and sessile in their 

 gonangia. 



Fig. 45. Fig. 46. 



FiQ. 45.— Medusiform person (Saraia), one of the Anthomedusa, detached from a 

 hydioid colony of the family Oorynidce. b, the long manubrimn, bearing (as 

 an exception) medusiform bads; o, mouth. 



Fia. 46. — ^MediMitorm person, one of the Anthomedmee, 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. 



FiQ. 47. View of the oral surface of one of the Leplomedusce (.Irene pellmida, 



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

 M, manubrium ; ot, otocysts ; re, the four radiating canals ; Ve, the Telnm. 



The CdlyptoUastea of Allman, Slcmotoka of Cams, and Oampanu- 

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

 they give rise to free medusse, give rise to those termed Zeptomedusce 

 by Haeckel, corresponding to the Thaum/intiadce and Sucopidx of 

 Gegenbaur's system. The calyptoblastic hydroid Zeptosoyphits,yrhich, 

 according to Allman, gives rise to a Idzzia-Vike medusa {Antho- 

 medusce), is the only recorded exception to this correspondence. 

 The ^quoridce and. other medusae of similar structure have not been 

 traced into connexion with any hydriform trophosome, but we are 

 not justified therefore in concluding that they develop directly from 

 (he egg without hydriform phaise. The chief point distinguishing 

 the Leptomediisce as a lot from the Anthomedusce is the development 

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

 lar to that occupied by the same organs in Trachomedv^oe and 

 Scyphomedusce. Allman, however, considers the genital glands of 

 the LeptomeduscB, not as mere glands like those of Aurelia or 

 Charyldcea,- but as a, series of buds— a generation of aborted 

 medusae or sporosacs. In consequence he terms the medusa of the 

 Leptomediism 3,Ua.siackeme (or bud-producer), as distinguished from 

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



FiQ.48.— CSnTOorino (fierymia) liastaia, one of OieTraclumedutte. (After Haeckel.) 

 o, neiTe-iing; a', radial nerve ; S.tentaculocyst; c, circular canal; c, radiating 

 canal ; j", ovary ; h, peronia or cartilaginous process ascending fiom the carti. 

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

 disc; six of these arc perradia),' six interradial, corresponding to the twelve solid 

 larval tentacles, resembling those of Cunitia; k, dilatation (stomach) of the 

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

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

 M, cai-tilaginous margin of tire disc covered by thread-cellB ; v, velum. 



Order 3. Trachomedusce, — Hydrovudmrn which have as 

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



Fig. 49. — Diagram of a vertical section of Carmarina hastata, 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 gastric 

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

 ovailes; ft, stomach (dilatation of the manubrium); Z, tongue-like process of 

 the gelatinous substance ; A, cartilaginous process ascending from the marginal 

 ring at the site of a tentaculocyst ; c, circular canal; 6, tentaculocyat ; v, 

 velum ; «*, carlilaginous marginal ring. (Fi-om Gegenbanr.) 



formed by endodermic cells as in Sa/pkomedtisce, and 

 ocelli may or may not be present on the tentaculocyst. 



