238 THE FORMS OF CELLS [cii. 



transitory that their study is only rendered possible by "instan- 

 taneous" photography: but this excessive rapidity is not an 

 essential part of the phenomenon. For instance, we can repeat 

 and demonstrate many of the simpler phenomena, in a permanent 

 or quasi-permanent form, by splashing water on to a surface of 

 dry sand, or by firing a bullet into a soft metal target. There is 

 nothing, then, to prevent a slow and lasting manifestation, in 

 a viscous medium such as a protoplasmic organism, of phenomena 

 which appear and disappear with prodigious rapidity in a more 

 mobile liquid. Nor is there anything peculiar in the "splash" 

 itself; it is simply a convenient method of setting up certain 

 niotions or currents, and producing certain surface-forms, in a 

 liquid medium, — or even in such an extremely imperfect fluid as 

 is represented (in another series of experiments) by a bed of sand. 

 Accordingly, we have a large range of possible conditions under 

 which the organism might conceivably display configurations 

 analogous to, or identical with, those which Mr Worthington has 

 shewn us how to exhibit by one particular experimental method. 

 To one who has watched the potter at his wheel, it is plain 

 that the potter's thumb, like the glass-blower's blast of air, 

 depends for its efficacy upon the physical properties of the 

 medium on which it operates, which for the time being is essentially 

 a fluid. The cup and the saucer, like the tube and the bulb, 

 display (in their simple and primitive forms) beautiful surfaces of 

 equilibrium as manifested under certain limiting conditions. 

 They are neither more nor less than glorified "splashes," formed 

 slowly, under conditions of restraint which enhance or reveal 

 their mathematical symmetry. We have seen, and we shall see 

 again before we are done, that the art of the glass-blower is full 

 of lessons for the naturalist as also for the physicist: illustrating 

 as it does the development of a host of mathematical configura- 

 tions and organic conformations which depend essentially on the 

 establishment of a constant and uniform pressure within a closed 

 elastic shell or fluid envelope. In like manner the potter's art 

 illustrates the somewhat obscurer and more complex problems 

 (scarcely less frequent in biology) of a figure of equilibrium which 

 is an ofen surface, or solid, of revolution. It is clear, at the same 

 time, that the two series of problems are closely akin; for the 



