I2b THE SENSES OF ANIMALS 



the little fresh-water i/y^ra, are among the least complex of the 

 Metazoa, and have few special sense organs. A sea-anemone 

 is built of a vast number of cells, yet the animal functions 

 as a whole, and the actions of the individual cells are co- 

 ordinated. The co-ordination is effected because some of the 

 cells are specialized as nerve cells, each of which is drawn out 

 into a number of threads called axons, which nearly touch the 

 threads from neighbouring nerve cells to that a nerve net- 

 work extends throughout the body. The ends of the threads 

 from different nerve cells do not actually join, but lie very 

 close to each other forming a synapse. Special sensory cells are 

 packed in between the cells forming the skin that lines both 

 the outer and inner surface of the body, and axons from the 

 nerve network lie almost in contact with their inner ends. The 

 inner ends of some of the cells of the outer skin can contract 

 when they are suitably stimulated and thus function as 

 muscular tissue; they too are in near-contact with the 

 threads of the nerve-net. 



The combination of sensory cells connected by the nerve 

 network to the muscle cells enables the sea-anemone's in- 

 numerable cells to act in concert so that the animal behaves 

 as an individual. The cells are an orderly army, and not a 

 disorganized rabble, through the mediation of the nerve 

 network. 



One of the well-known sea-anemones of the British coasts 

 is Taelia felina, often several inches in diameter, and 

 coloured with streaks and flecks of green, red, white, brown, 

 and grey. The stalk below the disc of tentacles is covered 

 with warty lumps which led the Victorian naturalist P. H. 

 Gosse (the father in Edmund Gosse's Father and Son) to give 

 it the English name of Dahlia Wartlet. He also remarked 

 that the colours "are very sportive, and scarcely two speci- 

 mens can be found alike". In i860 Gosse published the first 

 book on British sea-anemones, a classic work illustrated with 

 beautiful coloured plates made from his own water-colours 

 of the living animals. There was a widespread interest at 

 that time in the "wonders of the shore", mainly as a result 

 of Gosse's numerous books on natural history. His book on 

 anemones, although a scientific treatise, was also intended 

 to help the amateur naturalist to identify the anemones he 



