THE INTEGUMENT 679 



can demonstrate for himself. The question that presents itself is simply 

 this : Does it follow that because a bird has all the characteristics of a 

 reptile, plus some additional features, that, therefore, it had reptile an- 

 cestors? 



If one accept the so-called Haeckelian law of Biogenesis, that each 

 individual in the embryonic stage passes through the adult stages of the 

 race to which it belongs, then such a conclusion is valid; but, if we re- 

 member that all this so-called law means is that all forms pass through 

 similar stages, the higher forms then continuing, while the lower ones 

 remain stationary, another interpretation is still more valid. And our 

 difficulty is by no means lessened when we remember that biologists at 

 large are agreed that acquired characteristics are not transmitted. What, 

 then, becomes of even a reasonable explanation of how any modifications 

 can be carried on from parent to offspring? 



Still further, we have seen from Professor de Vries' work that all 

 newly appearing structures may be but the return of some recessive por- 

 tions which have long lain dormant, while in the so-called rudimentary 

 structures there is always the alternative of considering such structure 

 an overgrowth or a hypertrophy of some smaller organ valuable at some 

 time in embryonic life, or, it may even be a true remnant of a structure 

 no longer needed by modern methods of life, modern foods and modern 

 environment. Or, still a third alternative suggested by Professor Bate- 

 son, that just as a complex 

 structure is the more com- 

 plex, the smaller and simpler 

 it can be made to appear, so 

 the original fertilized egg- 

 Fig ; 40 - cell, from which an entire 



Diagram to show growth of bone. A, animal recent- 

 ly fed madder which causes a layer of bone (black) to Vertebrate develops, is much 

 be colored by the dye ; B, no madder fed for a time, 



when a deposit of colorless bone on outside of colored more C O m p le X than the 



layer is formed ; C, later the outer layer becomes thick- / 1 i i_ j i_ 



ened and the inner layer is absorbed. Finally Completed DOdy, DC- 



cause the single cell had all the possibilities of the complete body within 

 its tiny self, and consequently, we are always really losing something 

 as development proceeds. 



What is meant by a normal development of a cell into what it is 

 later to become, is simply, that commonly, certain obstacles are removed 

 by which these possibilities can come forth. If then, either environment 

 (external or internal), food, atmosphere, position, injury, or chemical 

 stimulus removes certain factors which hold back growth, any such pos- 

 sible factor already present in the cell may come forth ; but its possibility 

 must have been already present in the primitive cell. 



This is well shown by the fa'ct that normally the skin finishes growth 

 at a certain time, but if a portion of skin is torn, the injury stimulates 

 the connective-tissue cells which then divide and fill the wound with 

 scar-tissue, that is, the original injury removes an obstacle to such con- 



