Marvels of Pond-Life. 37 



harder than the inner layer. These layers are scverallv 

 called ectoderm and endoderm. They may be cut and 

 grafted like trees, and if turned inside out, the new 

 inside digests and assimilates as well as the old. 

 Whether any form of consciousness can belong to 

 creatures which have no distinct nervous system is 

 open to doubt, but it would seem probaljle from their 

 movements that food and light afford them something 

 like a pleasurable sensation in a very humble degree. 

 If we were sufficiently acquainted with the secrets of 

 molecular combination we might discover that the 

 various functions of these simple organisms were dis- 

 charged by different 2^articles, although it is only in 

 higher creatures that muscular particles are aggregated 

 into muscles, or nerve particles into nerves. 



Having examined the general appearance and pro- 

 ceedings of the hydra, let us cut off a tentacle, or take 

 a small specimen and gently crush it by pressing down 

 the cover of the live box, and place the object so pre- 

 pared under a power of about three hundred linear. If 

 we then illuminate it with a moderate quantity of oblique 

 light, we shall discover round the edge of the tentacle 

 a number of small cells or capsules, from some of 

 which a very slender wire or thread will be emitted."'^ 

 These are the stinging organs of the polyp, and 

 resemble those which jNIr. Gosse has so ably elucidated 

 in the sea anemones. Some writers have endeavoured 

 to show that they are not stinging organs at all, but so 

 large an amount of evidence to the contrary is accu- 

 mulated in Mr. Gosse's ' Actinologia Britannica,' 



* See page 34, C and D. 



