294 



LAWS OF VARIATION. 



Chap. XXIV. 



point the limb was cut off, the deficient part, and no more, was exactly 

 reproduced. Even with man, as we have seen in the twelfth chapter 

 when treating of polydactylism, the entire limb whilst in an embryonic 

 state, and supernumerary digits, are occasionally, though imperfectly 

 reproduced after amputation. When a diseased bone has been removed' 

 a new one sometimes " gradually assumes the regular form, and all the 

 " attachments of muscles, ligaments, &c, become as complete as before/' 3 

 This power of regrowth does not, however, always act perfectly: the 

 reproduced tail of a lizard differs m the forms of the scales from the normal 

 tail : with certain Orthopterous insects the large hind legs are reproduced 

 of smaller size : 4 the white cicatrice which in the higher animals unites 

 the edges of a deep wound is not formed of perfect skin, for elastic 

 tissue is not produced till long afterwards. 5 " The activity of the nisus 

 " formativus " says Blumenbach, "is in an inverse ratio to the ase of the 



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" organised body/' To this may be added that its power is greater in 

 animals the lower they are in the scale of organisation ; and animals low 

 in the scale correspond with the embryos of higher animals belonging to 

 the same class. Newport's observations 6 afford a good illustration of this 

 fact, for he found that " myriapods, whose highest development scarcely 

 carries them beyond the larvae of perfect insects, can regenerate limbs and 

 antennae up to the time of their last moult;" and so can the larvae of true 

 insects, but not the mature insect. Salamanders correspond in develop- 

 ment with the tadpoles or larvae of the tailless Batrachians, and both 

 possess to a large extent the power of regrowth ; but not so the mature 

 tailless Batrachians. 



Absorption often plays an important part in the repairs of injuries. 

 When a bone is broken, and does not unite, the ends are absorbed and 

 rounded, so that a false joint is formed ; or if the ends unite, but overlap, 

 the projecting parts are removed. 7 But absorption comes into action, as 

 Virchow remarks, during the normal growth of bones ; parts which are 

 solid during youth become hollowed out for the medullary tissue as the 

 bone increases in size. In trying to understand the many well-adapted 

 cases of regrowth when aided by absorption, we should remember that 

 most parts of the organisation, even whilst retaining the same form, 

 undergo constant renewal ; so that a part which was not renewed would 

 naturally be liable to complete absorption. 



Some cases, usually classed under the so-called nisus formativus, at first 

 appear to come under a distinct head ; for not only are old structures 

 reproduced, but structures which appear new are formed. Thus, after 

 inflammation " false membranes," furnished with blood-vessels, lymphatics, 

 and nerves, are developed ; or a foetus escapes from the Fallopian tubes, 

 and falls into the abdomen, " nature pours out a quantity of plastic 

 " lymph, which forms itself into organised membrane, richly supplied with 

 " blood-vessels," and the foetus is nourished for a time. In certain cases of 



3 Carpenter's 'Principles of Comp. 

 Physiology,' 1854, p. 479. 



4 Cliarlesworth's < Mag. of Nat. Hist. ' 

 vol. i.. 1837, p. 145. 



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5 Paget, « Lectures on Surgical Patho- 

 vol. 



»/' 



i. p 



239. 



c Quoted by Carpenter, ' Comp. Phj rs - 

 p. 479. 7 Paget, « Lectures/ &c., p. 257. 





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