72 



HYDROZOA 



have uo otooysts, but only ocelli (Ocellata<) t or they have 

 otoeysts (tig. 11) (eetodornml sues), four, eight, or over a 

 Immlred, not homologous with tentacles, and sometimes in 

 addition ocelli ( rttifiilahr). The radial ontoric canals uro 

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

 whilst the marginal tentacles of the disc uro either few or 



FIR. 4R. FiR. 40. 



Km. . MediisWirm pewon (.tirtfoV one of the .4 K/AiiinnfMir. dotachd from 

 hydroM eolonj of the family <\uyin,f,r. b, the long mamibriwn, bearing ( 

 H txcvpiton) m*4\ulfonn I>U,N ; n, mouth. 



Ki. 4ti. Mctlualform |H<raon, one of tho .4MiuMi<ihu<r, detached from n hvdro... 

 colony of .SJOKSII-JW^. Ocelli are awn HI the base of tho tentacles, nml also (as 

 mi MtOtpttUU gnwps of niodusllorm build. 



very numerous. Tho genital glands always arc placed in 

 the course of the radial canals of the disc (not in tho utanu- 

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

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

 charge is uncertain. 



Ku>. 4T. View of (hi' oral surface of on<> of the l.rp(amnlt<r (/raw prihlrida, 

 HaecMk, to show the numerous tentacles iul tho otocysts. p, gvnltal glands; 

 .V. ntauubrlnm; o.', olocysts; tv, the four fnilUtlni; oniU.i; V, . the \t'lum. 



The ( WyutoMii.tfVii of Allnuni, SbfMtohi of Cams, and Ctui>i>tinu- 

 lariir of authors form a wcll-tnarkoil group of hydivids which, when 

 they )t' Vl> ri* 1 * l' vt> iiuxlusio, give rise to those termed Lfptometiu&f 

 by Havkel, oorivsjiotidinj! to the ThiimnaHtiaiitr and Eufopiiltv of 

 r's system. The oalyptoWastie hydroid /.<-^(-i//iAii, t \vhi 1 -h, 

 to Allmnn. gives rise to * /.term-like medusa (AttMo- 

 is the only recorded exception to tliis correspondence. 

 The sKym>riiit and other meihisiv of similar stvuetuiv hv* not been 

 tracwl into wnnexion with any hydritorm tmphosome, but we are 

 not justified theivfoiv incoiioUuliiij; tluit they develop directly from 

 fhe egsj without hydriform phs<>. The chief jx>int distingxiishing 

 the /.<^*>irtfN.w its A lot from til* jtntiit>mt<lus<r is the drvolopniout 

 nf the gonorativt> Kxlies in the radial canals. This pi^sition is simi- 

 lar to that occupied, by the same organs in Tmi-tiMiitiiuMt *&A 

 iSci/j>At>WfWi(.s<r. Allman, howewr, considei's the gvnitl glands of 

 the IsptonuilHsiT, not as n>en> glands like those of Aurtlia or 

 ("Atirw/i^ni, but as a series of buds a generation of aborted 

 medusso or sporosaes. In consequence he terms the medusa of tlie 

 LtptOMmiHMi*. blastocheme ^or bud-pnxluco^. as distinguished l'n>m 

 ftonoeheme (or geniUl-pnxluccr). In sup)K>it of this view, 



Allnmn (Aftmograuh, 1874) adduces tho various remarkable case* 

 of production <>!' buds by mnlus.r \\hi,-h Intve been reeorded (tig. 

 H, -l.'i, -lii), mid, furtlu'f, the M-I\ >tukiiif; Niiiiilnrity between the 

 Htructure of a lobe of the genital gland of Obelin and a spui-osae 

 MII-II us we liml in Jlt/i/nictiiiiii. It seems necesaury to n.v. ].i 

 Alliuan's view on this miillir, unless we are iire|uired tn uliatiilnn 

 the homology of sporosacii with medusa* in the case of hydriform 

 |iersons. 



The eolonies of hydriform persons of the present group dilfer inter 

 e acconling to the arrangement of the cups or hydiotheeie. In 

 Pluiniilnnait they aro sessile, and all on one side of a branch ; in 

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

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

 mcduMii'orm persons sometimes remain abortive and sessile in their 

 gomuigia. 



F1.48. fWiwm'i'<i(Wi'r^oi')Ain(nM,oneof thc7>'oc*<*iwir. (Aflei Haul,, 1 t 

 .1. none nut. ', rmlUI imTi' ; A, trntnouloryit ; f, flrcukr cnl; t, vmlmtiiin 

 etmul ; if", ovwry ; A. ini-viilH or ejutlluniiuuis imH'fM aDeoiultiiK hoin the cintt. 

 luminous nmrjjin of tho disc centvipetHllv In the outer Mivfnce of the jcll\ hke 

 dlde; six of those HIV |>enmlial, *1\ interradiiil, coirfspotulinu to the twelve soldi 

 lrvnl leutticled, iTseniblltiK tho^o of CNNI'IHI; Jt, tlllatatlon (sieintu'h) of the 

 nmimbrlum; /, ji'lly of tli* dltr: I', iiMiiubrluni : /, tentacle (hollow and 

 tertiary, *.*., tutiH-ili'it by lx i>errillal ami six Intemullnl solid larval tentacle*) ; 

 n, rarlbngluoud innrcln of the disc covered by thread-cells ; i\ velum. 



Order 3. Trtifhomtdustr, JIy<iroinrdi<f<r which haT6 aa 



sense-organs tcntttcnlocysts. The nd'liilis { \\. r.M ;i n> 



FlG. 49. Plajrr.im of a vertlcul section of OiMiirt<i AtuMfn. (lassjnp on thft 

 ri^lu thronch the \\hoK' length ef a r;uli:itini; cannl, and on the left thn>Uh 

 the outprad lobe of an ovary. /, gelatinous snbstamt' of the disc and siistric 

 talk (muiubriumV. r, radial Ini; canal; n, its outer, rt, its Inner wall; 17, 

 ovaries; *, atomach (illlatation of the manubrlum): 7, tongue-like process of 

 the gelatinous substance; *, cartilaKinous puvess ascending tioiu the tnavginal 

 ring at the site of a tentaculoevst : c. ciivnlar can.-il; A, tentaculocyst ; r, 

 velum; *, cartilaginous marginal ring. (From Gegvnbanr.) 



formed by eudodermic cells as in Scitpfwntfihisa?, and 

 ocelli may or may not be present on the tentaculocyst. 



