EEPTILES AND AMPHIBIA 171 



In order to test the mechanical effect of the resistance of 

 the water on the surface of a cylindrical body moved from 

 side to side, as the body of a fish or newt is moved, I made 

 the following experiment: I took a cylindrical penholder 

 and coated it with a thin layer of sealing-wax, making the 

 layer as uniform as possible, so that the surface was still 

 cylindrical. I then moved the penholder to and fro in hot 

 water, holding one end of it in my hand. The heat of the 

 water softened the wax, and after continuing the movement 

 for some minutes a ridge of wax was formed in a position 

 exactly corresponding to the vertical fins of a tadpole's tail, 

 or of a fish, that is to say in a plane perpendicular to that 

 in which the motion took place. Continuing the motion 

 some minutes longer, I found that a thin lamina of sealing- 

 wax was formed along the penholder above and below in the 

 vertical plane, the motion being horizontal. This lamina 

 was more than half an inch high. The cylinder of wood 

 with its uniform coating of wax was thus converted in about 

 five minutes into a structure corresponding, as exactly as 

 the difference of materials would allow, to the structure of 

 the tail of a newt or fish, leaving fin-rays of course out of 

 consideration. The similarity between the laminae of wax 

 produced, and the fin membrane of a newt, tadpole, or fish 

 is very remarkable. The wax does not pass off gradually 

 from the penholder with a thick base and narrow edges. 

 The origin of the lamina is quite sharply defined, just as is 

 the origin of the membranous fin of a fish or newt, and the 

 base of the lamina forms a very distinct angle with the 

 surface of the penholder. 



This is an experiment which anyone can repeat for himself 

 with very little time or trouble, by means of materials 

 usually at hand on any writing-table. Simple as the ex- 

 periment is, it seems to me to be of far-reaching importance. 

 Unless it can be disproved that growth of the skin takes place 



