NATIONAL ACADEMY BIOGRAPHICAL MEMOIRS — VOL. VIT 



points of view may be summarized in his oft-quoted remark 

 of Aristotle, that the "essence of a living thing is not what it 

 is made of nor what it does, but why it does it," or, as he ex- 

 presses it elsewhere, "the essence of a living thing is not proto- 

 plasm, but purpose;" and in the further statements which he 

 draws from Berkeley, that "nature is a language," that "phe- 

 nomena are appearances," and that "natural laws are not arbi- 

 trary nor necessary, but natural, i. e., neither less nor more 

 than one who has the data has every reason to expect." His 

 system of philosophy was profoundly influenced by the writings 

 of George Berkeley; his language resembles in its force and 

 beauty the essays of Huxley, but his application of these to the 

 foundations of science is his own. 



On his fiftieth birthday, March 25, 1898, his former students 

 united in presenting to him an oil portrait of himself (see 

 page 71), together with a congratulatory address, and at the 

 end of his book on the "Foundations of Zoology" he added 

 on this date the following note : 



For you who have, at this time, for my encouragement, called your- 

 selves my students, I have written this book which has been my own so 

 long that I should part with it with regret, did I not hope that, as you 

 study the great works to which I have directed you, you may still call 

 me teacher. If you are indeed my students, you are not afraid of hard 

 work, so in this day of light literature, when even learning must be 

 made easy, you must be my readers, and you must do double duty; for 

 I take the liberty of a teacher with his pupils, and ask that, after you 

 have read the book, you will some day read it again ; since I hope that 

 what may seem obscure, may, on review, be found consistent and 

 intelligible. 



Much that he has written still seems to me obscure, although 

 I have read it more than once, but I bear in mind his parting 

 request, and in the meantime profit by that which I do under- 

 stand, and am charmed by the classical and almost poetical 

 diction in which it is written. Whatever one may be inclined 

 to say of his conclusions and theories, it cannot be denied that 

 in an age when biological investigators have been content with 

 discovering phenomena, he attempted to go back of phenomena 

 to their real meaning and significance and to point out the rela- 

 tionship of these newly-discovered phenomena to the great cur- 



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