212 DR OTTO THILO. 



forms of spines are forthcoming, which for him formerly only 

 pointed to a difference in the outward appearance. But the 

 mechanician can see in these differences in the click mechanism 

 many natural devices. It is a striking fact that fish radiants 

 in two parts are more frequent than those in three parts, 

 and this shows clearly the difference between artificial and 

 natural mechanism. 



Eunning catch mechanisms in two parts can only be used 

 where they can be constantly overlooked and fixed. This con- 

 stant regulating is, for an animal, easy, through the help of 

 the muscles ; in machinery it is impossible. Here the click 

 mechanism in three parts only affords sufficient surety. Of 

 course this surety is attended with some inconvenience, and 

 although this is not important in many machines, still, some- 

 times the engineer must painfully feel his inability to make use 

 of the easily-used clicks in two parts, such as we admire in the 

 spines of a stickleback. Quick as lightning he can raise his 

 spines against an enemy and firmly hold them, and even when 

 dead they remain. In the clicks of the Monacanthus in three 

 parts such elasticity is not attainable and also not requisite. 

 These dull fish swim badly, and move their fins little back- 

 wards and forwards. They hold their fins either raised up or 

 perfectly laid down. We see, therefore, that the choice of the 

 click mechanism in nature is made exactly according to the 

 uses they are destined to fill. For these uses the click 

 mechanisms in two parts are better suited than those in three 

 parts. They are simpler, and therefore freer from functional 

 derangements than those in three parts. In the first place, 

 those in two parts offer fewer defects ; secondly, the removal of 

 causes of interruption in the simpler stops in two parts is easier 

 than in the more complex stops in three parts. Injury, inflam- 

 mation, and swelling must certainly occur in the joints of the 

 fins very frequently, as is shown by the broken and scarred 

 fins that one so often finds on fish. 



We see also in the click mechanisms of fish that nature, 

 through simplifying, prevents their deranging. And also here 

 the engineer can learn from nature through the simphcity of 

 his mechanism to avoid functional derangements. Naturally 

 he can only borrow from nature the primary idea for his 



