XI] IN VARIOUS ORGANISMS 495 



spires " of a snake, in the coils of a cuttle-fish's arm, or of a monkey's 

 or a chameleon's tail. 



Among such forms as these, and the many others which we 

 might easily add to them, it is obvious that we have to do with 

 things which, though mathematically similar, are biologically 

 speaking fundamentally different. And not only are they bio- 

 logically remote, but they are also physically different, in regard 

 to the nature of the forces to which they are severally due. For 

 in the first place, the spiral coil of the elephant's trunk or of the 

 chameleon's tail is, as we have said, but a transitory configuration, 

 and is plainly the result of certain muscular forces acting upon 

 a structure of a definite, and normally an essentially different, 

 form. It is rather a position, or an athfude, than a form, in the 



Fig. 238. A Foraminiferal shell (Globigerma). 



sense in which we have been using this latter term ; and, unlike 

 most of the forms which we have been studying, it has little or no 

 direct relation to the phenomenon of Growth. 



Again, there is a manifest and not unimportant difference 

 between such a spiral conformation as is built up by the separate 

 and successive florets in the sunflower, and that which, in the 

 snail or Nautilus shell, is apparently a single and indivisible unit. 

 And a similar, if not identical difference is apparent between the 

 Nautilus shell and the minute shells of the Foraminifera, which 

 so closely simulate it ; inasmuch as the spiral shells of these latter 

 are essentially composite structures, combined out of successive 

 and separate chambers, while the molluscan shell, though it may 

 (as in Nautilus) become secondarily subdivided, has grown as 

 one continuous tube. It follows from all this that there cannot 



