22 ' LECTURES 



Attention was first turned toward the question 

 of the unity of plan in the case of the verte- 

 brata by the poet Goethe, who, early in the present cen- 

 tury pointed out the fact that the'premaxillary bone or 

 that element of the skull which supports the upper 

 incisor teeth, occurring, as it probably does in all back- 

 boned animals, should occur in man. This he finally 

 demonstrated to be true, and its demonstration, taken in 

 connection with the theory of Oken on the vertebrated 

 nature of the entire skull, a lecture given by that trans- 

 cendent anatomist at a time when Goethe was present, 

 turned the attention of all leading anatomists of the 

 time to making comparative studies of animals, often 

 with the view of elucidating some obscure structure in 

 the organization of man. Since the time of which I 

 speak comparative morphologists have made, without 

 any exaggeration, thousands upon thousands of such com- 

 parisons, and the truth of the unity of plan of structure 

 among the vertebrata is as well established as is the form 

 of the earth. Botanists find that essentially the same holds 

 true in the vegetable world. So that were one to fully 

 study any single well-chosen plant, in all 

 its details, he would practically possess the 

 key to the knowledge of the morphology 

 of plants, both living and extinct. So also for the 

 physiology of plants; so also for the physiology of animals, 

 a full comprehension of physiologic laws, as exemplified 

 in a tortoise, are found to obtain with the same exactitude 

 in an elephant. In other words it has come to be known 

 that certain broad laws concerning such matters possess a 

 general application throughout both the vegetable and 

 animal kingdom. 



Another great subject has come to be very largely 

 understood through the labors of the biologists of this 

 century, and that is the geographical distribution of 

 plants and animals, both for those now existing and for 

 those which existed during former ages of the world but 

 are now extinct. This is a very important field as we 

 shall hereafter see. 



Still another vast problem of prime importance has 

 been elaborated within the last hundred years, and 

 to it the millions of facts drawn from all departments 

 of biology lend substantial support. I refer to the 

 doctrine of the generation of living beinars; the prob- 

 able origin of life upon the globe; the development of 

 the individual, the development of the triba; the history 

 of animals and plants throughout all time; and, finally, a 



