462 



SCIENCE 



[N. S. Vol. XXXVIII. No. 979 



suspected correlations and thus bring ever 

 so many more homoplasies in its wake. 



Function is always present in living 

 matter ; it is life. It is function which not 

 only shapes, but creates the organ or sup- 

 presses it, being indeed at. bottom a kind of 

 reaction upon some stimulus, which stimuli 

 are ultimately all fundamental, elementary 

 forces, therefore few in number. That is 

 a reason why nature seems to have but few 

 resources for meeting given "require- 

 ments" — to use an everyday expression, 

 which really puts the cart before the horse. 

 This paucity of resources shows itself in 

 the repetition of the same organs in the 

 most different phyla. The eye has been 

 invented dozens of times. Light, a part of 

 the environment, has been the first stim- 

 ulus. The principle remains the same in 

 the various eyes ; where light found a suit- 

 ably reacting material a particular evolu- 

 tion was set going, often round about, or 

 topsy-turvy, implying amendments; still, 

 the result was an eye — in advanced cases 

 a scientifically constructed dark chamber 

 with lens, screen, shutters and other ad- 

 justments. The detail may be unimpor- 

 tant, since in the various eyes different 

 contrivances are resorted to. 



Provided the material is suitable, plastic, 

 amenable to prevailing environmental or 

 constitutional forces, it makes no difference 

 what part of an organism is utilized to 

 supply the requirements of function. You 

 can not make a silk purse out of a sow's 

 ear, but you can make a purse, and that is 

 the important point. The first and most 

 obvious cause is function, which itself may 

 arise as an incidental action due to the 

 nature of the material. The oxidizing of 

 the blood is such a case, and respiratory 

 organs have been made out of whatever 

 parts invite osmotic contact of the blood 

 with air or water. It does not matter 

 whether respiration is carried on by eeto- 



or by endodermal epithelium. Thus are 

 developed internal gills, or lungs, both of 

 which may be considered as referable to 

 pharyngeal pouches; but where the outer 

 skin has become suitably osmotic, as in the 

 naked Amphibia, it may evolve external 

 gills. Nay, the whole surface of the body 

 may become so osmotic that both lungs and 

 gills are suppressed, and the creature 

 breathes in a most pseudo-primitive fashion. 

 This arrangement, more or less advanced, 

 occurs in many Urodeles, both American 

 and European, belonging to several sub- 

 families, but not in every species of the 

 various genera. It is therefore a case of 

 apparently recent isotely. 



There is no prejudice in the making of 

 a new organ except in so far that every 

 organism is conservative, clinging to what 

 it or its ancestors have learned or acquired, 

 which it therefore seeks to recapitulate. 

 Thus in the vertebrata the customary place 

 for respiratory organs is the pharyngeal 

 region. Every organism, of course, has an 

 enormous back history ; it may have had to 

 use every part in every conceivable way, 

 and it may thereby have been trained to 

 such an extent as to yield almost at once, 

 like a bridle-wise horse to some new stim- 

 ulus, and thus initiate an organ straight to 

 the point. 



Considering that organs put to the same 

 use are so very often the result of analo- 

 gous adaptation, homoplasts with or with- 

 out affinity of descent, are we not justified 

 in accusing morphology of having made 

 rather too much of the organs as units, as 

 if they were concrete instead of inducted 

 abstract notions? An organ which changes 

 its function may become a unit so different 

 as to require a new definition. And two 

 originally different organs may come to 

 resemble each other so much in function 

 and structure that they acquire the same 

 definition as one new unit. To avoid this 



