POLYPIFERA. 



347 



longitudinal set : both are flattened, and exhibit no trans- 

 verse striation. In some Actiniae, such as A. mesembryan- 

 tkemum, bright blue sacs are placed at the edges of the oral 



Fig. 189. Hydra, wiih its tentacles displayed and magnified, adhering to a stalk 

 of Anacharis alsinastrum. 



disc, while in A.gemmacea, A. sessilis, &c. clear spots are 

 scattered over the integument, which have been regarded 

 as apertures or tubercles; M. Hollard, however, states, that 

 these are imperforate Ampullce, possessing a kind of bila- 

 biate mouth, surrounded by a sphincter- like arrangement of 

 muscular fibres. Any foreign body introduced into these 

 ampullse is seized and forcibly held ; or if the finger be 

 placed within reach, it gives the sensation of a very fine 

 rasp passing over it. The margins of the radiate tentacles 

 of the young animal are surrounded by cilia ; the gastric 

 epithelium is likewise ciliated, and doubtless secretes a 

 powerfully solvent fluid. The majority of the Actinia? 

 are oviparous, the young being developed from ova within, 

 and evacuated by the mouth : they are also capable of 

 multiplication by budding, and occasionally by fission, 

 while their power of restoring themselves after muti- 



