1050 THE THEORY OF TRANSFORMATIONS [ch. 



Holmes who first shewed this curious parallel between the operations 

 of the glass-blower and those of Nature, when she starts, as she so 

 often does, with a simple tube*. The alimentary canal, the arterial 

 system including the heart, the central nervous system of the 

 vertebrate, including the brain itself, all begin as simple tubular 

 structures. And with them Nature does just what the glass-blower 

 does, and, we might even say, no more than he. For she can expand 

 the tube here and narrow it there; thicken its walls or thin them; 

 blow off a lateral offshoot or caecal diverticulum; bend the tube, 

 or twist and coil it; and infold or crimp its walls as, so to speak, 

 she pleases. Such a form as that of the human stomach is easily 

 explained when it is regarded from this point of view ; it is simply 

 an ill-blown bubble, a bubble that has been rendered lopsided 

 by a trammel or restraint along one side, such as to prevent its 

 symmetrical expansion — such a trammel as is produced if the glass- 

 blower lets one side of his bubble get cold, and such as is actually 

 present in the stomach itself in the form of a muscular band. 



The Florence flask, or any other handiwork of the glass-blower, 

 is always beautiful, because its graded contours are, as in its living 

 analogues, a picture of the graded forces by which it was conformed. 

 It is an example of mathematical beauty, of which the machine-made, 

 moulded bottle has no trace at all. An alabaster bottle is different 

 again. It is no longer an unduloid figure of equilibrium. Turned 

 on a lathe, it is a solid of revolution, and not without beauty ; but 

 it is not near so beautiful as the blown flask or bubble. 



The gravitational field is part of the complex field of force by 

 which the form of the organism is influenced and determined. Its 

 share is seldom easy to define, but there is a resultant due to gravity 

 in hanging breasts and tired eyelids and all the sagging wrinkles 

 of the old. Now and then we see gravity at work in the normal 

 construction of the body, and can describe its effect on form in 

 a general, or qualitative, way. Each pair of ribs in man forms 

 a hoop which droops of its own weight in front, so flattening the 

 chest, and at the same time twisting the rib on either hand near its 

 point of suspension f. But in the dog each costal hoop is dragged 



* Cf. Elsie Venner, chap. ii. 



t See T. P. Anderson Stuart, How the form of the thorax is partly determined 

 by gravitation, Proc. R.S. xlix, p.l43, 1891. 



