HYDROZOA CRASPEDOTA. 763 



In the first-named the manubrium divides, and then the bell. In 

 Pkialidium a second manubrium appears as a bud at the base of the 

 first, and fission then takes place between the two. A third may be 

 similarly formed in the course of a radial canal. Gastroblasta has the 

 number of manubria increasing progressively by budding on the radial 

 canals, and fission occurs between the oldest and second oldest. Sexual 

 products were observed in the two last-named 1 . The detachment by fission 

 of the end of a growing branch has been observed in some Campanularidae'. 

 and in one instance the fixation of the detached portion, the formation of a 

 hydranth, and subsequently of a colony 2 . Gemmation is universal in the 

 hydroid form, Protohydra only excepted : and is not uncommon in Medusae, 

 for the most part belonging to the Anthomedusae. In Hydra, Microhydra, 

 and Tiarella the hydroid form thus produced is set free, but the first- 

 named may be temporarily colonial, the individual not only producing 

 more than one bud, but its buds other buds in their turn before detach- 

 ment. In all other instances the hydroid buds remain attached to one 

 another, constituting a colony. They originate from the hydrocope of the 

 first hydranth, and afterwards from the coenosarc in a definite manner. 

 The buds in a hydroid colony which develope into sexual zooids may take 

 origin from the hydrorhiza when the hydranths do so, from the branches 

 of a colony, then occupying either the same or a different position to a 

 hydranth, from the peduncle of a normal hydranth, from its hydrocephalis, 

 from a blastostyle, or from a special peduncle of unknown significance 

 (Tubularia, Corymorpha, Monocaulus)*. The buds borne by a Medusa in- 

 variably develope into a Medusa : they may be situated on the manubrium, 

 on the tentacles or at their bases, on the radial canals, or circumfe- 

 rential canal, and gemmation may be continued through more than one 

 generation. 



The sexes are as a rule separate. Hydra and Eleutheria are hermaph- 

 rodite : abortive ova occur in the male of Gonothyrea Loveni. Male and 



1 Lang thinks that Davidoff's Phialidium variable is not the Medusa usually so-called, but a 

 younger form of his G. Raffaelci. A species, Gastroblasta timida, has been described by Keller in 

 Z. W. Z. xxxviii. pp. 622 et seqq. It has four manubria, but fission was not observed. See on the 

 whole subject Lang's paper in J. Z. xix. 1886. 



2 I. e. in Allman's Schizocladium ramosum ; see op. cit. ante, pp. 151-3, Fig. 61. Detachment 

 has been observed in Obelia flabellata and 0. (Laomedea) geniculata : Wagner, Wirbellosen des 

 Weissen Meeres, Leipzig, 1885, p. 69. Hincks thinks it occurs in Campanularia neglecta (A. N. H. 

 (4), x. 1872, p. 391), and Allman in Corymorpha nutans (op. cit. p. 153). Hydranths have been 

 observed with several oral cones in Cordylophora lacustris (Price, Q. J. M. xvi. 1876), and two 

 hydranths on the same peduncle occasionally occur in Hydractinia echinata (Wagner, op. cit. PL 

 I. Fig. 8) ; whether fissiparously produced or not is unknown. 



3 The medusa sometimes takes origin in the same place as does a hydranth, e. g. from the 

 peduncle of a hydranth, the Tubularians, Dendroclava, Bougainvillea, some species of Perigonimus ; 

 from the stem of a colony, P. muscoides ; from the hydrorhiza, some species of Perigonimus, the 

 Campanularian Eucopella. As a rule it originates from the hydrocephalis of a hydranth, or from a 

 blastostyle as in Podocoryne and most Campanularidae. 



