762 THE ANIMAL KINGDOM. 



the two Campanularian families Plumularidae and Sertularidae \ and the 

 following stages may be enumerated (Weissman): (i) Medusoid. There are 

 no tentacles, and as a rule no velum, no organs of special sense, nor mouth 

 to the manubrium, detached when ripe, e.g. Pcnnaria 2 '. (2) Sessile Medusoid. 

 The bell has either incomplete canals or none at all, but there is a bell- 

 mouth and cavity, e. g. Ttibularia, female Cladocoryne. (3) Sessile Gono- 

 phore. Bell devoid of cavity and mouth, but with a gastral lamella, subum- 

 brellar and manubrial ectoderm laminae, e. g. Clava, Hydractinia, Phimu- 

 laria. (4) Sessile Gonophore. Bell with gastral lamella, subumbrellar and 

 manubrial ectoderm forming a single lamina if present : female Campanula^ 

 ria> Opercularella, Halecium. (5) Sporosac Sporophore. A sessile gonophore 

 without trace of medusoid structure, e.g. Cordylophora, male Campanularia 3 . 

 The term * spadix ' is applied to the central closed endodermic structure 

 representing the manubrial cavity in a gonophore or sporosac. It is 

 sometimes branched, e.g. in Cordylophora. An alteration in the place 

 and mode of origin of the generative products usually accompanies these 

 changes, but not always to the same degree in the two sexes : see pp. 

 767-8, post. 



As to the Hydrocorallina, the generative products of Millepora are de- 

 veloped in small capsules in the course of the coenosarcal canals ; of Sty- 

 lasteridae in a sporosac formed in the course of the same canals and lodged 

 in an ampulla or cavity of the coenosteum 4 . 



Asexual reproduction takes place by fission or gemmation. Fission 

 is rare. It occurs in the hydroid Protohydra Leuckarti, where it is binary 

 and transverse ; in Polypodium, where it is longitudinal (infra, p. 766) ; and 

 in certain Leptomedusans, Stomobrachium mirabile ( = a young form of 

 Mesonema coerulescens), in Phialidium variabile, and Gastroblasta Raffaelei. 



1 The medusae produced by Syncoryne (jCoryne) nrirabilis are said by L. Agassiz to be set free 

 in March, but in April to be sessile and more or less arrested in development ; cf. Allman, op. cit. 

 ante, p. 278, and lit. cited. Campamilaria volubilis is said by Du Plessis to bear medusae in 

 summer, gonophores in winter (A. N. 41 (2), p. 412). See also Wagner, Wirbellosen des Weissen 

 Meeres, Leipzig, 1885, p. 78. 



2 The Meconidium of Gonothyrea is a medusoid which is not detached ; and the male is more 

 arrested than the female. See Weismann, op. cit. ante, pp. 135-7, J 39> an d Allman, op. cit. 

 ante, pp. 55-8, Fig. 28. 



3 The Tubularian Dicoryne conferta has a remarkable free swimming ciliated sporosac with two 

 solid tentacles attached to the base of the spadix. The spermatozoa surround the spadix, but in the 

 female there are only two ova, one on either side of it. See Allman, op. cit. ante, p. 226. In 

 Serttilarella polyzonias the gonophore is suppressed and the genital products ripen in the walls of a 

 blastostyle : see Weismann, op. cit. p. 166, note p. 252, p. 265. On the nature of the blastostyle 

 cf- P- 75 7> ante, and note 2. 



The development of a sporosac after discharging the generative products into a hydranth has 

 been described in Cordylophora by Allman, and L. Agassiz has observed a similar case in Rhizogefan : 

 cf. Allman, op. cit. p. 204. Some doubt is perhaps permissible on the subject. 



* Quelch states that there are ampullae in Millepora Murrayi \ see Reef Corals, Challenger 

 Reports, xvi. p. 192 ; or Nature, xxx. p. 539. 



