viii AUTHOR'S PREFACE 



fact, I have added to the principal title of the whole work, "The 

 Cell and the Tissues," the secondary title " Outlines of General 

 Anatomy and Physiology." Further, I am able to say, as I said 

 of my Text-book of Embryology : Man and Mammals, that it has 

 been produced in close connection with my academical labours. 

 The contents of the first part, in which I have endeavoured to 

 sketch a comprehensive picture of the structure and life of the 

 cells, were the subject of two lectures which I delivered at the 

 University of Berlin four years ago, under the titles of " The Cell 

 and its Life," and " The Theory of Generation and Heredity." 



Besides wishing to communicate to a larger circle of readers 

 the views which I had often expressed verbally, I had the further 

 desire of giving a comprehensive review of results obtained by 

 private research, some of which were recorded in various Journals, 

 whilst others appeared in the six papers on " The Morphology and 

 Physiology of the Cell," which I wrote in conjunction with my 

 brother. 



Finally, a third reason which induced me to write this book 

 was, that it should supplement my Text-book of Embryology : Man 

 and Mammals. In it I have endeavoured to state the laws which 

 underlie animal formation, according to which cells, formed from 

 the fertilised egg-cell by repeated division, split up, as a result 

 of unequal growth, the complicated layers and outgrowths into 

 germinal folds, and finally into individual organs. 



In addition to the distribution of cell-masses and to the 

 arrangement of cells, that is to say, in addition to the morpho- 

 logical differentiation, a second series of processes, which may be 

 grouped together under the term histological differentiation, takes 

 place during development. By means of histological differentia- 

 tion, the morphologically separated cell material is capable of 

 performing the different functions into which the vital processes 

 of the developed collective organism may be divided. 



In my Text-book of Embryology, it was impossible to deal ex- 

 haustively with the second or more physiological side of the pro- 

 cess of development. The Anatomy and Physiology of the Cell, 

 forms a necessary complement to it, as I mentioned above. This 

 will be especially noticed by the student in the first part of 

 the book, which deals with the cell alone. For not only is there, 

 in the seventh chapter, a detailed description of the anatomy and 

 physiology of reproduction, which is ultimately a cell pheno- 

 menon, but at the end of the book, in the ninth chapter, there 



