December 13, 1912] 



SCIENCE 



809 



animals is determined and controlled by 

 plants, or that of plants by animals? 

 There is no more ground for asserting that 

 the organization within a subordinate or- 

 gan of the individual plant or animal is 

 determined and controlled by another or- 

 gan from which the first receives some 

 form of energy or some substance. It is 

 clear that the secretion of the thyroid 

 afEects the integument. In the absence of 

 that secretion the integument becomes al- 

 tered in character. But it does not become 

 disorganized. Its cellular elements re- 

 main organized as integumentary tisKSue, 

 but with changes in the details of that 

 organization. There is no ground for at- 

 tributing the fundamental fact that certain 

 cells are organized as integumentary cells 

 to the influence of the thyroid secretion or 

 any other secretion contained in the body 

 fluids. 



The whole process of organic develop- 

 ment may possibly be described in terms 

 of hormones. If that shall come to pass, 

 a considerable degree of complication will 

 have been added to our conception of the 

 process of ontogeny and our information 

 will have been vastly enlarged. May such 

 an achievement be regarded as bringing 

 us one step nearer our goal of understand- 

 ing the nature of the organization upon 

 which development rests? Only in the 

 sense that it is one step of an infinite num- 

 ber of steps of that pa,rticular kind which 

 separate us from the goal. To discover a 

 mechanics of development in terms of hor- 

 mones is to bring within our cognizance 

 additional facts of organization. No such 

 description will reveal to us the essence of 

 organization. I do not mean to discredit 

 the search for mechanism. Just so far as 

 mechanism exists we must know about it, 

 for we seek the complete truth about or- 

 ganisms. It is conceivable that practical 



benefits of inestimable importance may fol- 

 low from a complete knowledge of organic 

 mechanism. But the nature and origin of 

 mechanism are not to be found by discov- 

 ering more mechanism. 



It appears possible that the development 

 of the lens of the vertebrate eye depends 

 upon some effect proceeding from the optic 

 vesicle. But even if this relation is fully 

 proved, the problem of the development of 

 the lens is by no means solved. The invagi- 

 nation of the ectoderm to form a lens may 

 depend upon contact of the optic vesicle 

 with the ectoderm, or upon the action of a 

 substance given off by the optic vesicle. 

 Any such relation between the two struc- 

 tures is open to either of the two interpre- 

 tations which are before us. The invagi- 

 nation of the lens ectoderm involves what 

 looks to us like concerted action upon the 

 part of numerous cells. We may suppose 

 that each cell possesses an inherent mech- 

 anism which, under the conditions in which 

 the cell normally finds itself, compels the 

 cell to play just that particular part in 

 lens development which it does play. This 

 inherent mechanism depends, we may sup- 

 pose further, upon germinal preformation 

 which in the last analysis, if this view is 

 carried to its logical consequences, depends 

 upon chance combinations of atoms and the 

 accidents of selection. It is a peculiarity 

 of the environment in which the cells live 

 that at a certain time an effect is produced 

 upon them by a group of underlying cells 

 (assuming the relation between the optic 

 vesicle and the lens to have been proved). 

 It happens that this effect introduces pre- 

 cisely the conditions needed to set going 

 the separate mechanisms in the several 

 cells. Upon this view the organization 

 within the ectodermal layer — its organiza- 

 tion as ectoderm and such more or less 

 localized organization within it as renders 



