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 Actinozoa, 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 reparative 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) " 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." 

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

 insensible motion which was absorbed in producing certain 



