222 LEISURE-TIME STUDIES. 



A second authority who framed an explanation of the 

 causes of likeness was Bonnet, who maintained that lost 

 parts were reproduced by germs contained in the nearest 

 portions of the injured body ; whilst by his theory of em- 

 boitement it was held that each germ was in itself the re- 

 pository of countless other germs, these bodies being stored 

 up in a quantity sufficient for the reproductive needs of 

 countless generations. Professor Owen's explanation de- 

 pends upon the recognition of the fact that certain of the 

 cells of the germ from which the living being springs pass 

 into its body, and there remain to transmit to its successors 

 the material characters which it has acquired ; whilst, also, 

 the repair of injuries, and the propagation of new beings 

 by budding and like processes, are explained on the sup- 

 position that these germ-cells may grow, increase, and 

 operate within the organism which they are ultimately 

 destined to propagate. Lastly, Mr. Darwin has come to 

 the solution of heredity with his theory of Pangenesis, which 

 may be said to avail itself of all that is reasonable and 

 probable in the explanations just discussed, and also to 

 include several new and important ideas of which the older 

 theorists took no account. 



As paving the way for an understanding of this and 

 other explanations of the law of likeness, we may briefly 

 glance at some of the chief facts with reference to the 

 structure and intimate composition of living beings, with 

 which microscopic study has made us acquainted. When 

 the anatomist or physiologist seeks to unravel the com- 

 plications of human structure, or when, indeed, he scrutinises 

 the bodies of all animals, save the very lowest, he finds that 

 each organ or tissue of the body is composed of certain 

 minute vesicles or spheres, to which he gives the name of 

 cells (Fig. 33). Cells, in fact, are the units of which the 

 bodily whole is composed. Nerves thus resolve themselves 

 under the microscope into fibres, and the fibres, in turn, are 

 seen to originate from cells. Muscles similarly originate 

 from muscle-cells. Each tissue, however compact it may 



