PREFACE. 



Ix this little book an attempt has been made to 

 determine and explain the nature of some of the 

 most important changes which are characteristic 

 of and peculiar ' to living beings. Technical terms 

 have been as far .as possible avoided. Many of the 

 matters I have thoug'ht it desirable to^ consider are, 

 however, complicated and intricate, indeed of a 

 character not gcDerally discussed in text books, and 

 I fear that, in some instances, I have failed to 

 render what I have tried to convey as clear and as 

 intelHgible as I desired. Most of the inferences I 

 have drawn concerning very difi&cult questions rest 

 upon actual facts of minute research, but I have 

 ventured to speculate upon s»me matters which 

 are at present beyond the sphere of observation. 



The reader will probably admit that the first part 

 of his task is not a difficult one, but as he progresses 

 I fear he will find the book becomes more difficult to 

 read. In the last four lectures some rather abstruse 

 points in physiology have been bi'ought under the 

 student's notice, but the facts upon which the con- 

 clusions so far deduced have been based are recorded 

 and explained. 



