December 20, 1912] 



SCIENCE 



853 



pates in an important way in the develop- 

 ment of an organ, but it contributes noth- 

 ing of specific character to that organ inas- 

 much as tissue of the same type would play 

 precisely the same role in the development 

 of any other organ. It is therefore essen- 

 tially a tissue process, being one which in 

 no way bears the impress of any higher or- 

 ganization of the individual. The inherent 

 propensity of an epithelium for investing 

 a surface illustrates the tissue process. 



In yet another instance we see a group 

 of tissue elements undergoing changes 

 which result in the establishment of some 

 specific feature of an organ, such as the 

 alveolus of a gland, or a Bowman's capsule 

 of the kidney. Not every group of elements 

 belonging to the type of tissue concerned 

 would, even if placed in the physical situa- 

 tion occupied by the group under considera- 

 tion, give rise to that same structure. It is 

 clear, however, that a certain structure may 

 upon occasion be formed by a group of ele- 

 ments other than that which would nor- 

 mally give rise to it. The tissue elements 

 which normally do form a certain structure 

 of high order, and those which in emergency 

 can do so, must either contain within them- 

 selves or encounter in their environment an 

 energy-complex which determines their ac- 

 tivity. Something, therefore, must be 

 added to or impressed upon the organiza- 

 tion of an epithelial tissue or else some- 

 thing corresponding to the organization of 

 the higher system must dominate the tissue 

 prganization. In this case, then, we have 

 an example of a developmental event which 

 owes its occurrence to energetic factors be- 

 longing to that grade of organization cor- 

 responding to those larger structural com- 

 plexes which, in the ordinary anatomical 

 sense, we call organs. 



Finally we observe that organs develop 

 in such a way that certain larger structural 

 complexes are established. The several 



organs come to have, in a great variety of 

 ways, very definite relations one to another. 

 Especially conspicuous are the spatial re- 

 lations which result in a certain body plan 

 and general form. These larger relations 

 and peculiarities characterize an organic 

 unit higher in grade than the organ, 

 namely, the organism as a whole or the 

 individual or, as Haeckel names it, the per- 

 son. We meet here precisely the same prob- 

 lem which we have met at every other level 

 of organization. It is conceivable that ab- 

 solutely indifferent cells exist — cells pos- 

 sessing no organization beyond that repre- 

 sented in the structural substratum com- 

 mon to all cells. When a cell becomes a 

 tissue cell the fundamental cell organiza- 

 tion must have been modified or something 

 must have been added to it or something 

 must dominate it. Further, a tissue as 

 such, while possessing certain definite 

 habits of growth, is indeterminate in form. 

 In an epithelium one dimension, thickness, 

 is approximately determined. In muscle 

 tissue no dimension is determined. When 

 a tissue becomes shaped into an organ or 

 some part of an organ, the fundamental 

 tissue organization must have been modi- 

 fied or something must have been added to 

 it or something must dominate it. Still 

 further there is no universal necessity gov- 

 erning the larger relations which exist 

 amongst organs. We need only compare 

 individuals of different species to see that 

 similar and corresponding organs may be 

 related to one another in a variety of ways 

 so that individuals very unlike in body 

 plan and general form result. Somewhere 

 in ontogeny must exist energetic factors re- 

 sponsible for these larger features which 

 characterize the individual as a whole. 

 These factors may consist in modifications 

 of organizations of lower orders or in some- 

 thing added to them, or they may consist 

 in some energy-complex which transcends 



