6o THE POPULAR SCIENCE MONTHLY. 



effort that carries belief to an opposite extreme changing approval 

 into a disapproval that is entire instead of partial. Hence, in the one 

 case, as in the other, we must infer that the resulting obstacle to well- 

 balanced conclusions can become less only as social evolution becomes 

 greater. 



THE BORERS OF THE SEA. 



"A /TANY stories are current as to how inventors have borrowed or 

 -i-VLL stolen their ideas from Nature, and there has been much in- 

 genious discussion as to whether hints thus appropriated are properly 

 patentable. Boring is an example of natural processes that have 

 been thus used by art, and it is remarkable that the lowest creatures 

 are the most skilful mechanics in this particular. An eminent living 

 inventor, who has made a fortune out of a patent auger, hit upon the 

 method followed by the most successful insects which bore into hard 

 wood. And so we are assured that the celebrated engineer Brunei, 

 in constructing the Thames Tunnel, but imitated the shell-lined burrow 

 of the Teredo navalis, or Ship-worm. This mollusk in shape resem- 

 bles a worm, and surrounds itself with a shell open at both ends. 

 From the mouth it can protrude its short foot, and the other extremity 

 of its body; the " tail " is bifurcated, one prong being the inspirator 

 and the other the expirator tube of the siphon which constitutes the 

 animal's nutritive apparatus. 



It has long been a subject of controversy among naturalists how 

 the Ship-worm and other mollusks of the same family bore their way 

 into the rocks and timbers which they penetrate. As regards the 

 Pholades, for instance, Mr. Robertson, who kept these animals alive in 

 their chalky burrows, and studied their habits with the closest atten- 

 tion, found that when burrowing they make a half-revolution of their 

 shell to the right, and then back to the left, after the manner of a car- 

 penter using a brad-awl. The Pholas is a bivalve, club-shaped, and 

 the outer surface of its shell is covered with small teeth in curves, and 

 resembling the face of a rasp. These teeth would naturally seem well 

 suited for the purpose of boring, yet all naturalists are not agreed on 

 this point. Tims, some hold that the animal secretes an acid sol- 

 vent, which causes the material in which it is burrowing to decay. 

 Then only is it that, securing itself with its sucker-like foot, it works 

 itself from right to left, and vice versa, to widen the passage. But 

 Mr. Gwynn Jeffreys, as stated in the December number of The Popu- 

 lar Science Moxthlt, is of opinion that the foot, which he says is 

 charged with siliceous particles, is the true boring apparatus of all the 

 conchifera, and acts like the leaden wheel of the lapidary. 



The history of the development of the Teredo is thus given by M. 



