WASTE AND REPAIR. 219 



proof being that the disease occurs most frequently among 

 those engaged in laborious handicrafts, and usually attacks 

 first the muscles which have been most worked. 



There has yet to be noticed another kind of repair — that, 

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

 the Ilydrozoa 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 

 Vertehrata also, as lizards, can develop new limbs or new tails, 

 in place of those which 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 

 disappears where the organization is highest. And though 

 we cannot say that in the intermediate stages there is a con- 

 stant inverse relation between reparative power and degree 

 of organization ; yet we may say that there is some approach 

 to such a relation. 



§ 63. There is an obvious and complete harmony between 

 the first of the above inductions and the deduction which 

 follows immediately from first principles. We have already 

 seen (§23) "that whatever amount of power an organism 



