760 THE ANIMAL KINGDOM. 



possess vesicular otocysts ; their generative products ripen on the sub- 

 umbrella in the course of the radial canals, which are in number from 4, 6, 

 8, 16,32, 80, to several hundreds, and they are derived from Campanularian 

 Hydroids. In both groups the Medusa may after its detachment grow in 

 size, develope additional radial canals, tentacles, &c., and it may become 

 sexual before its full development is attained. 



The bell of the Anthomedusae is, as a rule, of greater depth than 

 breadth, conical or a four-sided pyramid in shape, and of a firm con- 

 sistence l . Meridional ridges or a network composed chiefly of cnidoblasts 

 may be present on the exumbrella. The velum is broad. The manubrium 

 is cylindrical with a simple mouth and is surrounded by the genital pro- 

 ducts in the Codonidae : usually quadrangular in cross section in the other 

 families, the genital products being variously arranged in bands. The 

 mouth is furnished with four lobes in the Tiaridae ; four solid capitate 

 simple or branched oral tentacles in the Margelidae ; and in the Cladone- 

 midae it varies, resembling one or other of the three families named 2 . Ten- 

 tacles to the bell may be entirely absent (Amalthaeidae\ or there may be 

 only one (Euphysidae) ; there are occasionally two, e. g. Gemmaria, Ctenaria, 

 but usually at least four, and when thus restricted in number they corre- 

 spond to the ends of the radial canals. Their number may be increased in 

 the Tiaridae, Margelidae and some Cladonemidae^ the additional tentacles 

 springing from the circumferential canal. They are sometimes grouped in 

 bunches, and in the Cladonemidae are either feathered or branched. Their 

 root is bulbous, and the eye is situated on this bulb, usually on its outer 

 aspect, but on its inner in those species that habitually carry the tentacles 

 reflexed, e. g. in Lizzia. Most Antkomedusde are small, some Codonidae 



and Cladonemidae not exceeding in. The Tiaridae are of fair size, 



and some species of Turris and Tiara attain a diameter of ij in. 



The Leptomedusae contrast with the Anthomedusae in the following 

 points. The bell is flat, its breadth greatly exceeding its depth ; it is rela- 

 tively soft, and hence assumes very different forms during contraction, and 

 may even be reversed, as not infrequently happens in Obelia. Exumbrellar 

 ridges are rare. The velum is feebly developed. The manubrium does 

 not project much : the mouth has usually four lobes, often of some length : 

 the atrium is quadratic or polygonal, and the radial canals spring from its 

 angles 3 . The latter vary from four (Eucopidae), eight (Melicertidae, &c.), 



1 In Sarsia the subumbrella separates from the gastral lamina along eight lines so as to form 

 eight closed pouches. See the description of S. tubulosa by F. E. Schulze in his ' Syncoryne Sarsii] 

 Leipzig, 1873, pp. 15-16. 



2 Complete absence of the manubrium and mouth has been observed in individuals of a 

 Bougainvillea: Mereschkowsky, A. N. H. (5), iii. 1879. 



3 The manubrium is exceedingly small in Obelia and Aequorea, and is absent in Staurostoma 

 and Staurophora, in which the mouth is a cruciform slit. Cf. Haeckel, op. cit. ante, pp. 130, 

 148. 



