OUE BODILY FEAME. 27 



combinations of millions, constitute the " cellular- 

 state," our body. All these cells spring from one 

 simple cell, the cytula, or impregnated ovum, by con- 

 tinuous subdivision. The general structure and com- 

 bination of the tissues are the same in man as in the 

 other vertebrates. Among these the mammals, the 

 youngest and most highly-developed class, take prece- 

 dence, in virtue of certain special features which were 

 acquired late. Such are, for instance, the micro- 

 scopic texture of the hair, of the glands of the skin, 

 and of the breasts, and the corpuscles of the blood, 

 which are quite peculiar to mammals, and different 

 from those of the other vertebrates ; man, even in 

 these finest histological respects, is a true mammal. 



The microscopic researches of Albert Kolliker and 

 Franz Leydig (at Wiirzburg) not only enlarged our 

 knowledge of the finer structure of man and the 

 beasts in every direction, but they were especially 

 important in the light of their connection with the 

 evolution of the cell and the tissue ; they confirmed 

 the great theory of Carl Theodor Siebold (1845) that 

 the lowest animals, the Infusoria and the Ehizopods, 

 are unicellular organisms. 



Our whole frame, both in its general plan and its 

 detailed structure, presents the characteristic type of 

 the vertebrates. This most important and most 

 highly-developed group in the animal world was first 

 recognised in its natural unity in 1801 by the great 

 Lamarck ; he embraced under that title the four 

 higher animal groups of Linne — mammals, birds, 

 amphibia, and fishes. To these he opposed the two 

 lower classes, insects and worms, as invertebrates. 

 Cuvier (1812) established the unity of the vertebrate 

 type on a firmer basis by his comparative anatomy. 



