410 THE FORMS OF TISSUES ETC. [ch. viii 



attempt to grapple with. The stock-in-trade of mathematical 

 physics, in all the subjects with which that science deals, is for the 

 most part made up of simple, or simplified, cases of phenomena 

 which in their actual and concrete manifestations are usually too 

 complex for mathematical analysis ; and when we attempt to 

 apply its methods to our biological and histological phenomena, 

 in a prehminary and elementary way, we need not wonder if we 

 be limited to illustrations which are obviously of a simple kind, 

 and which cover but a small part of the phenomena with which 

 the histologist has become familiar. But it is only relatively that 

 these phenomena to which we have found the method applicable 

 are to be deemed simple and few. They go already far beyond 

 the simplest phenomena of all, such as we see in the dividing 

 Protococcus, and in the first stages, two-celled or four-celled, of 

 the segmenting egg. They carry us into stages where the cells 

 are already numerous, and where the whole conformation has 

 become by no means easy to depict or visualise, without the help 

 and guidance which the phenomena of surface-tension, the laws 

 of equilibrium and the principle of minimal areas are at hand 

 to supply. And so far as we have gone, and so far as we can 

 discern, we see no sign of the guiding principles failing us, or of 

 the simple laws ceasing to hold good. 



