94 Trans. Acad. Sci. of St. Louis. 



has attracted much interest from the educated world at large, 

 owing to the practical importance of the question for soci- 

 ological and educational problems. 



In the latter part of his life, Darwin admitted the possibil- 

 ity of the Lamarckian factors, though strenuously denying 

 them in his earlier writings. Herbert Spencer and Romanes 

 in England, Haeckel in Germany and the American school of 

 palaeontologists have been the strongest advocates of Neo- 

 Lamarckianism, while the all-sufficiency of Natural Selection 

 has been stoutly upheld by Wallace, but above all by Weis- 

 mann and his followers. Although Natural Selection stands 

 upon a firmer footing than perhaps it has ever stood, the 

 general attitude among biologists is that, although the Neo- 

 Lamarckians have not made good their claim and have ad- 

 vanced no convincing experimental proof of the inheritance of 

 " acquired characters," it is still possible that these factors, 

 or yet some undiscovered ones, may have operated with 

 Natural Selection to bring about adaptations and the origin of 

 species. The discussion has been largely of an a priori nature 

 and little or no advance had been made toward a settlement ; 

 and the majority of biologists, I think, are willing to look 

 upon it as an open question for the future to decide, if it is 

 ever to be decided. During the past few years, however, a 

 serious attempt has been begun to carefully study the origin 

 of variations, without any bias towards one theory or another, 

 in the hope that the question of whether variations are deter- 

 minate or not may be settled. Already some valuable results 

 have come from this work, done almost entirely in this coun- 

 try, and it has given promise of becoming a most important 

 branch of zoological investigation. 



III. THE CELL DOCTBINE. 



Here we must leave the history of organic evolution and 

 look for a moment at the advance made in another great de- 

 partment of zoological science, a development which has taken 

 place almost independently of evolutionary views and entirely 

 in the nineteenth century. I refer to the development of the 

 so-called cell-theory which has created the science of cytology 



