SJ88 Dr Coldstream on the Structure and 



figured in fig. 19, the dotted lines surrounding which, mark the 

 original size of the pile represented), these, as well as the 

 nuclei of the branches, stand out in relief, dissected, as it were, 

 out of the softer materials which had surrounded them. Al- 

 though many workings approach very near one another at the 

 same depth from the surface, yet they preserve their original 

 direction so well, that they seldom or never open into one an- 

 other. 



Such are the results and consequences of the limnoria's appe- 

 tite for the woody fibre ; and having, by the means, and with 

 the circumstances above described, procured its natural food, we 

 may imagine, although we cannot see, how it uses its strong 

 mandibles in the comminution of the particles of the wood, so as 

 to fit them for being submitted to the digestive powers of the 

 stomach. 



Of the subsequent processes of chylification and assimilation, 

 nothing is known. And I have already stated that the circula- 

 tion has hitherto escaped my notice. There remains for me, 

 therefore, under this head, only to add the few facts relating to 

 the function of respiration which I have collected. 



When the animal is at rest in sea-water, the branchiae are 

 constantly fluttering with a slow motion, being alternately 

 moved out from the ventral surface, and then closely adpressed 

 against it, twenty or thirty times in a minute. The current pro- 

 duced in this way is about equal to the length of the body. 

 When any particles of dust clog the branchiae, the posterior pair 

 of legs is used to disencumber them. In swimming, the bran- 

 chiae are moved with much greater rapidity, also when the ani- 

 mal is placed in fresh water. The current is then considerably 

 longer. The limnoria continues to live for several hours in fresh 

 water. When the motions of the branchiae become languid, the 

 internal layer only is put in motion. On being taken out of the 

 water, it moves with extreme slowness, but lives for many hours. 

 Its branchial lamellae remain motionless. 



IV. History of the Ravages committed hy the Limnoria. 

 The circumstances connected with the erection of the Bell- 

 Rock Lighthouse are so well known, that it is unnecessary for 

 me to enter into particulars regarding the position and arrange- 



