OP ANIMALS. 27 



the solids. The areolar or cellular tissue, which forms the 

 greater part of the body, is very soft and contractile. The body 

 is traversed by an internal cavity, in which the aliments are 

 received. This cavity as well as the exterior surface, is invest- 

 ed with a membrane or skin which limits and envelops the 

 remainder of the body. There are in many animals circulating 

 vessels which convey, in certain determined directions, the 

 nutritive substance found in the intestine, into every part of 

 the body; organs of respiration, in which this matter is sub- 

 mitted to the action of the atmosphere, and secretory organs, 

 in which a part of this matter is separated from the mass. 

 They have genital organs which generally consist in a cavity 

 from which the germs are detached and expelled. Finally, 

 in most animals, there are muscles to execute the apparent 

 movements, senses to receive the impressions of external ob- 

 jects, and a nervous system consisting in cords or filaments, 

 having one of their extremities immersed and expanded in the 

 integuments and muscles, and the other swelling into enlarge- 

 ments or ganglia more or less considerable. 



12. The solids, or organs of animals, have for their prin- 

 cipal base the cellular tissue, a soft, extensible and contractile 

 substance, easily permeated by liquids. Condensed on the 

 two surfaces of the body, it forms on the exterior, the skin, 

 and on the interior, the mucous membranes or the internal 

 skin. It is this very same membrane, the skin, variously dis- 

 posed, which constitutes the organs of respiration, secretion 

 and generation. It also forms the senses. Hollowed into 

 ramified canals, in the parietes of which it possesses a consi- 

 derable consistence, the cellular tissue constitutes the vessels. 

 This same substance variously modified, without losing how- 

 ever its distinctive characters, forms also several other kinds 

 of organs in animals. The muscular fibre constitutes a second 

 kind of solid, essentially differing from the cellular tissue, be- 

 cause in the midst of this soft substance which forms the com- 

 mon mass, linear series of microscopic globules are to be ob- 

 served; this muscular fibre contracts whenever irritated. The 

 substance of the nerves is formed also of globules, but different 

 from those which compose the muscles; it transmits to nervous 



