WASTE AND REPAIR. 175 



namely, by which injured or lost parts are restored. Among 

 the Hydrozoa it is common for any portion of the body to re 

 produce the rest ; even though the rest to be so reproduced 

 is the greater part of the whole. In the more highly-organ 

 ized Adinozoa, the half of an individual will grow into a 

 complete individual. Some of the lower Annelids, as the 

 Nais, may be cut into thirty or forty pieces, and each piece will 

 eventually become a perfect animal. As we ascend to higher 

 forms, we find this reparative power much diminished, though 

 still considerable. The reproduction of a lost claw by a 

 lobster or crab, is a familiar instance. Some of the inferior 

 Vertebrata also, as lizards, can develop new limbs or new 

 tails, in place of those that have been cut off ; and can even 

 do this several times over, though with decreasing complete 

 ness. The highest animals, however, thus repair themselves 

 to but a very small extent. Mammals and birds do it only 

 in the healing of wounds ; and very often but imperfectly 

 even in this. For in muscular and glandular organs, the 

 tissues destroyed are not properly reproduced, but are re 

 placed by tissue of an irregular kind, which serves to hold 

 the parts together. So that the power of reproducing lost parts 

 is greatest where the organization is lowest ; and almost dis 

 appears where the organization is highest. And though we 

 cannot say that between these extremes there is a constant in 

 verse relation between reparatiA^e power and degree of organ 

 ization ; yet we may say that there is some approach to 

 such a relation. 



63. There is a very obvious and complete harmony be 

 tween the first of the above inductions, and the deduction 

 that follows immediately from first principles. We have 

 already seen ( 23) &quot; that whatever amount of power an 

 organism expends in any shape, is the correlate and equi 

 valent of a power that was taken into it from without.&quot; 

 Motion, sensible or insensible, generated by an organism, 13 

 insensible motion which was absorbed in producing certain 



