172 ZOOLOGY SECT. 



Nearly all are free-swimming in the adult state : some, however, 

 live on coral-reefs or mud-banks, and are found resting, in an 

 inverted position, on the ex-umbrella : and a few, such as Lucern- 

 aria, are able to attach themselves at will by a definite ex- 

 umbrellar peduncle. 



Considering the extremely perishable nature of these organisms, 

 and the fact that many of them contain not more than 1 per cent, 

 of solid matter, it is not to be expected that many of them should 

 have left traces of their existence in the fossil state. Nevertheless, 

 in the finely grained limestone of Solenhofen, in Bavaria, belong- 

 ing to the Upper Jurassic period, remarkably perfect impressions 

 of Jelly-fishes have been found, some of them readily recognisable as 

 Discomednsae. 



Many of the Scyphozoa are semi-transparent and glassy, but 

 often with brilliantly coloured gonads, tentacles, or radial canals. 

 In many cases the umbrella, oral arms, &c., are highly coloured, 

 and some species, e.g. Pelagia noctiluca, are phosphorescent. They 

 are all carnivorous, and although mostly living upon small 

 organisms, are able, in the case of the larger species, to capture 

 and digest Crustaceans and Fishes of considerable size. 



CLASS III. ACTINOZOA 



1. EXAMPLE OF THE CLASS A SEA-ANEMONE (Tcalia crassicornis). 



Sea-anemones are amongst the most abundant and best known 

 >f shore-animals. They are found attached to rocks, sea-weeds, 

 shells, &c., either in rock-pools or on rocks left high and dry by the 

 ebbing tide. Usually their flower-like form and brilliant colour 

 make them very conspicuous objects, but many kinds cover them- 

 selves more or less completely with sand and stones, and contract 

 so much when left uncovered by water, that they appear like soft 

 shapeless lumps stuck over with stones, and thus easily escape obser- 

 vation. Any of the numerous species will serve as an example of 

 the group : the form specially selected is the " Dahlia Wartlet " 

 ( Tcalia crassicornis), one of the commonest British species. 



External characters. Tealia (Fig. 124, A) has the form of a 

 cylinder, the diameter of which slightly exceeds its height. It is 

 often as much as 3 inches (8 cm.) across, is of a green or red colour, 

 and habitually covers itself with bits of shell, small stones, &c. It 

 is attached to a rock or other support by a broad sole-like base, 

 sharply separated from an upright cylindrical wall or column, the 

 surface of which is beset with rows of adhesive warts or tubercles : 

 at its upper or distal end the column passes into a horizontal plate, 

 the disc or pcristomc. In the middle of the disc, and slightly 

 elevated above its surface, is an elongated slit-like aperture, the 



