i6o 



THE FOOD OF ANIMALS 



ZOOPHYTES, JELLY-FISH, AND MILLEPORE CORALS 



(HYDROZOA) 



A simple example of this class is the common Freshwater 

 Polyp (Hydra) (see vol. i, p. 465), which is practically a living 

 stomach of cylindrical shape, attached by one end, which is 



closed, while in the 

 centre of the other is 

 a dilatable rounded 

 mouth, placed at the 

 apex of a conical pro- 

 jection. Around the 

 base of this projection 

 are arranged a num- 

 ber of hollow tentacles, 

 richly provided with 

 thread-cells, and cap- 

 able of being stretched 

 out for a considerable 

 distance in search of 

 prey. The branching 

 sea- weed -like struc- 

 tures known as Hy- 

 droid Zoophytes (fig. 

 414) are in reality 

 colonies of hydra-like 



individuals which capture prey by means of their tentacles. In 

 many cases such colonies give rise to Jelly- Fish or Medusae (see 

 vol. i, p. 479) comparable in shape to an umbrella, the mouth 

 being situated at the end of the handle. Other sorts of jelly- 

 fish arise by the transverse division of certain simple zoophytes, 

 and others again have no fixed stage in the life-history. In all 

 cases nettling-organs are present in great abundance, especially 

 upon slender tentacles with which the umbrella is fringed, and 

 upon lobes and filaments placed in the neighbourhood of the 

 mouth. 



MILLEPORE CORALS. A very interesting group of Hydrozoa 

 is that containing certain corals, of which the Millepore Coral 

 (Millepora) (fig. 415) may be taken as an example. This is a 

 colony, of which the shape depends upon the species, and it is 



Fig. 414. A Hydroid Zoophyte (Tubnlaria) 



