WALKER ON ORIGIN AND DISTRIBUTION OP MOLLUSCA. 43 



THE ORIGIN AND DISTRIBUTION OF THE LAND AND FRESH- 

 WATER MOLLUSCA OF NORTH AMERICA. 



BRYANT WALKER. DETROIT. 

 (Address of the Retiring- President of tlie Academy, delivered Dec. 26, 1895.) 



The origin of life has been a favorite topic for thought and discussion 

 among the philosophers from the earliest times, of which we have any 

 literary records. From the time when the mere struggle for existence 

 ceased to occupy the whole attention of primitive man, and the advance 

 of civilization afforded the leisure and opportunity for intellectual life, 

 the great problem of its own existence, and that of the world around it. 

 necessarily obtruded itself upon the thoughtful mind. 



There is scarcely a race or tribe of mankind, except perhaps those in 

 the very lowest stages of barbarism, who have not. at least some legend 

 or tradition as to the creation of the world and its inhabitants, and with 

 every advance in civilization there has been a corresponding widening of 

 the intellectual horizon, which has enabled the successive genera- 

 tions of man to put aside the crude imaginings of the savage for 

 the adoption of a better and more rational system of natural philosophy. 

 The evolution of a world's philosophy must always be a subject of the 

 greatest interest, and when the complete history of human knowledge 

 comes to be written, there will be no chapters exceeding in interest those, 

 which shall elaborate the rise and development of those great laws of 

 science, art, politics and religion, which are toda}^ considered to be the 

 fundamental principals of our modern civilization. 



In the centuries w^hich lie between Thales of Ionia and Darwin of 

 England, much has been written and many theories have been advanced 

 upon the origin of life, only to be thrown aside again by each succeeding 

 school of philosophy. And today, after twenty-five hundred years of 

 speculation and research, the question of origin of the ultimate principle 

 of life — the vital essence — is, from a scientific point of view, still un- 

 solved and apparently insolvable. But while the speculative minds of 

 the nineteenth century are still groping and grasping unsuccessfully 

 for the same will-o'-the-wisp, which danced before the Ionian phil- 

 osophers half a millennium before the Christian Era, there are others and 

 more practical phases of the question, to which the science of today 

 believes it has the key, and which can be made to yield their mysteries 

 to the patient seeker after scientific truth. 



The origin, not of life in the abstract, but of the manifold and varied 

 forms of animated nature, which now and in ages past have peopled 

 the world, is the fruitful field in which modern science has won her 

 choicest triumphs. 



The speculation of the early Greek philosophers in this subject, while 

 they may seem crude and too often absurd to our modern eyes, are re- 

 markable in many instances for their keen insight into nature and their 

 foreshadowing of those great principals of evolution and design, which 

 today mould the thoughts of the scientific world. Broadly speaking, how- 



