24 



POLYPIFERA. 



Fig. 27. 



Hydra fusca end of a tentacle extended, magnified. 



a, investing membrane ; b, nodosities ; c, prehen- 

 sile darts ; d, tactile cilia ; e, longitudinal, and /, 

 transverse muscular fasciculi. (After Corda.) 



Fig. 28. 



Hydra fusca. 



1, 2. Tactile cilia and their sacculi highly magni- 

 fied ; p, first sac ; q, second sac ; r, minute cavity ; 

 s, cilium. 



3. Prehensile apparatus highly magnified ; fi, 

 aperture ; i, epidermis of the tentacle ; k, first sac ; 

 /, second sac ; m, saucer-like body (vesica) ; n, 

 oval basis (hastifer) ; o, dart. 



4. Intestinal villus highly magnified ; /, foramen ; 

 g, cavity of the villus. 



5. Particles of fat or oil. (After Corda.) 



the sagittas are empoisoned, as an animal once 

 laid hold of by the Hydra very speedily dies. 



At the base of the tentacula, the open- 

 ing of the mouth is surrounded with lips 

 capable both of inflection and protrusion. 

 This lip is similar in structure to the ten- 

 tacles themselves, and is in like manner 

 provided with tactile appendages, and with 

 prehensile sagittae upon its external surface. 

 These lips, by their contraction, shut and 

 open the mouth at the pleasure of the Hydra, 

 and, when the size of the animal is taken into 

 the account, appear to be endowed with ex- 

 traordinary muscular force. The rest of the 

 body is quite devoid both of sagittae and of 

 tactile organs. 



The body of the Hydra, according to Corda, 

 is covered externally with a membrane that 

 consists of two layers, of which the exterior 

 (fig. 29, a) is composed of large cells, whilst 

 in the inner layer are contained the germina, 

 of which we shall immediately have to make 

 further mention. 



Between the skin and the alimentary canal 

 Corda announces the existence of a muscular 

 layer (fig. 29, 6), composed of dense cells, 

 which are coloured, and appear to be filled 

 with minute granules. 



The innermost layer of all (fig. 29, c), 

 from its position and texture, ought, accord- 

 ing to the same author, to be called the 

 villous coat (tunica vittosa). This stratum 

 lines the entire alimentary tract, from the 

 margin of the labial processes as far as the 

 anus, being divided at intervals by folds into 

 numerous compartments. The villi of which 

 this stratum consist are intimately connected 

 with the muscular layer ; their shape is cylin- 

 drical, but they are of two kinds, some being 

 perforated at their apex by a foramen, whilst 

 the others are close. Each of these villi 

 (fig. 28, 4) is a rounded, pellucid vesicle, the 

 walls of which are thick, and probably con- 

 tractile, and in those which are perforated 

 the perforation would seem to convey nu- 

 tritive matter into their interior. 



Behind the anal orifice there is a small, 

 hollow, and contractile membranous pro- 

 longation (fig. 29, <?), which constitutes the 

 sucker, or foot. 



ANTIIOZOA. 



AI.CYONID/K. The races of polypiferous 

 zoophytes which next offer themselves for our 

 examination may be described as consisting 

 of a common body or central mass, over the 

 surface of which are disseminated numerous 

 polypes, all of which contribute to the nutri- 

 tion of the community to which they belong. 

 In the first family, Alcyoninm, examples of 

 which are abundant on our own shores, the 

 substance of the polypary or general body, 

 which may frequently be picked up upon the 

 beach, appears tobe a shapelesslump of a tough 

 gelatinous substance, upon which, to an ordi- 

 nary observer, no indications of its wonderful 

 organization are apparent ; so that we cannot 

 wonder at its being so frequently passed by as 

 an object devoid of interest. On putting one 

 of these amorphous masses into a glass ot sea- 



