V] OF FIGURES OF EQUILIBRIUM 231 



capable of subsisting in equilibrium under the action of that force, 

 either of itself or subject to certain simple constraints. And as 

 yet we have limited ourselves to the case of a single surface, or 

 of a single drop or bubble, leaving to another occasion a discussion 

 of the forms assumed when such drops or vesicles meet and com- 

 bine together. In short, what we have said may help us to under- 

 stand the form of a cell, — considered, as with certain limitations 

 we may legitimately consider it, as a liquid drop or liquid vesicle ; 

 the conformation of a tissue or cell-aggregate must be dealt with 

 in the light of another series of theoretical considerations. In 

 both cases, we can do no more than touch upon the fringe of a 

 large and difficult subject. There are many forms capable of 

 realisation under surface tension, and many of them doubtless to 

 be recognised among organisms, which we cannot touch upon in 

 this elementary account. The subject is a very general one; it 

 is, in its essence, more mathematical than physical ; it is part of 

 the mathematics of surfaces, and only comes into relation with 

 surface tension, because this physical phenomenon illustrates and 

 exemplifies, in a concrete way, most of the simple and symmetrical 

 conditions with which the general mathematical theory is capable 

 of dealing. And before we pass to illustrate by biological examples 

 the physical phenomena which we have described, we must be 

 careful to remember that the physical conditions which we have 

 hitherto presupposed will never be wholly realised in the organic 

 cell. Its substance will never be a perfect fluid, and hence 

 equilibrium will be more or less slowly reached; its surface will 

 seldom be perfectly homogeneous, and therefore equilibrium will 

 (in the fluid condition) seldom be perfectly attained ; it will very 

 often, or generally, be the seat of other forces, symmetrical or 

 unsymmetrical ; and all these causes will more or less perturb the 

 effects of surface tension acting by itself. But we shall find that, 

 on the whole, these effects of surface tension though modified are 

 not obliterated nor even masked ; and accordingly the phenomena 

 to which I have devoted the foregoing pages will be found 

 manifestly recurring and repeating themselves among the pheno- 

 mena of the organic cell. 



In a spider's web we find exemplified several of the principles 



