6 NATURE'S TEACHINGS. 



turn over with the weight of the occupant, the next move 

 was evidently to lash two trunks side by side. 



Next would come the great advance of putting the trunks 

 at some distance apart, and connecting them with cross-bars. 

 This plan would obviate even the chance of the upsetting of 

 the raft, and it still survives in that curious mixture of the 

 raft and canoe, the outrigger boat of the Polynesians, which 

 no gale of wind can upset. It may be torn to pieces by the 

 storm, but nothing can capsize it as long as it holds together. 



Laying a number of smaller logs or branches upon the bars 

 which connect the larger logs is an evident mode of forming a 

 continuous platform, and thus the raft is completed. It would 

 not be long before the superior buoyancy of a hollow over a 

 solid log would be discovered, and so, when the savage could 

 not find a log ready hollowed to his hand, he would hollow 

 one for himself, mostly using fire in lieu of tools. The pro- 

 gress from a hollowed log, or " dug-out," as it is popularly 

 called, to the bark canoe, and then the built boat, naturally 

 followed, the boats increasing in size until they were developed 

 into ships. 



Such, then, is a slight sketch of the gradual construction of 

 the Boat, based, though perhaps ignorantly, on the theory of 

 displacement. Now, let us ask ourselves whether, in creation, 

 there are any natural boats which existed before man came 

 upon the earth, and from which he might have taken the idea 

 if he had been able to reason on the subject. The Paper 

 Nautilus is, of course, the first example that comes before the 

 mind ; but although, as we have seen, the delicate shell of the 

 nautilus is not used as a 'boat, and its sailing and rowing powers 

 are alike fabulous, there is, as is the case with most fables, a 

 substratum of truth, and there are aquatic molluscs which form 

 themselves into boats, although they do not propel themselves 

 with sails or oars. 



Many species of molluscs possess this art, but we will select 

 one as an example of them all, because it is very plentiful in 

 our own country, and may be found in almost any number. It 

 is the common WATER-SNAIL (Limncea stagnalis), which abounds 

 in our streams where the current is not very strong. Even in 

 tolerably swift streams the Limnaea may be found plentifully in 

 any bay or sudden curve where a reverse current is generated, 



