3 



THE YOUNG NATURALIST. 



EA ANEMONIES & CORALS, 



abstract of a Lecture by G. Brook, Esq., F.L.S. 



nettle, but generally they are harmless to us, but 

 may exercise a kind of benumbing influence upon 

 the prey which they capture. 



In the first class (Hydroidu) there is a body 

 , cavity as in fig. 23. The common fresh-water 



Fig. 21. — General Form of Sea Anemone. 



-IE order under which the sea anemones and 

 Is are included is called Coil enter ata, andcom- 

 ises many other classes besides the two named, 

 is divided into two sub-orders Hydrozoa and 

 tinozoa. The leading feature of the whole order 

 ithat the animals have a permanent mouth and a 

 estive cavity, which, however, has no outlet, 

 food refuse having to be ejected through the 

 )uth. Thus they present an intermediate form 

 ween the Protozoa, which have only a rudi- 

 ;ntary mouth, or none at nil, and those higher 

 ms of which I shall afterwards have to speak, 

 uich have an alimentary system entirely separate 

 m the general body cavity, in which the organs 

 ; contained. 



Fig. 23. 



Hydra is an example, it may be found in pools 

 attached to a plant or any foreign body by means 

 of a kind of disc. In its simple condition the 

 Hydra is a single oval sac with a cluster of tenta- 

 cles around the mouth, but the animal may in- 

 crease by budding, and thus become branched, 

 as in fig. 24. 



Fig. 22. 



Fig. 22 shews an ideal section of one of those 

 ;imals. The mouth is situated at B, and opens 

 a short canal into the body cavity c, which 

 mtains the few organs the animal possesses. On 

 outer skin there is generally some peculiar 

 ?ans termed thread-cells. These are cells which 

 ntain a filament or fibre coiled up, and which 

 be protruded sometimes to considerable 

 lgth. In a few species these filaments cause 

 istering on the human skin like the sting of a 



Fig. 24. 



It is curious to watch under the microscope the 

 tentacles twist round anything they catch, and 

 draw it towards the mouth in the centre. There 

 is one peculiar property about this animal, that 

 however much it is cut up, each piece develops 

 into a fresh Hydra. It also grows by budding, 

 and it can also develop a sort of eggs out of which 

 young animals are developed, which swim about 

 free for some time, and then settle down and at- 

 tach themselves to some leaf or floating matter 

 and grow into adult forms like the parents. Most 

 of the forms ©f the Hydroida are marine, and the 

 history of their development is very interesting 

 Many of the compound forms, such as are found 

 attached to stones, shells, &c, on the sea-shore, 

 have a sort of larval form which they pass through 



