858 



PROVISIONAL HYPOTHESIS 



Chap. XXVII 



amputated it was replaced by a perfect liinb.^^ The new 

 limbs in these cases bud forth, and are developed in the same 

 manner as during the regular development of a young animal. 

 For instance, with the Amhlystoma lurida, three toes are first 

 developed, then the fourth, and on the hind-feet the fifth, 

 and so it is with a reproduced limb.^° 



The power of re-growth is generally much greater during 

 the youth of an animal or during the earlier stages of its de- 

 velopment than during maturity. The larvae or tadpoles of the 

 Batrachians are capable of reproducing lost members, but 

 not so the adults. ^^ Mature insects have no power of re- 

 growth, excepting in one order, whilst the larvee of many kinds 

 have this power. Animals low in the scale are able, as a 

 general rule, to reproduce lost parts far more easily than those 

 which are more highly organised. The myriapods offer a good 

 illustration of this rule ; but there are some strange ex- 

 ceptions to it — thus Nemerteans, though lowly organised, are 

 said to exhibit little power of re-growth. With the higher 

 vertebrata, such as birds and mammals, the power is extremely 

 limited. ^^ 



In the case of those animals which may be bisected or 

 chopped into pieces, and of which every fragment will 

 reproduce the whole, the power of re-growth must be diffused 

 throughout the whole body. Nevertheless there seems to be 

 much truth in the view maintained by Prof. Lessona,^^ that 

 this capacity is generally a localised and special one, serving 

 to replace parts which are eminently liable to be lost in each 

 particular animal. The most striking case in favour of this 

 view, is that the terrestrial salamander, according to Lessona, 

 ^nnot reproduce lost parts, whilst another species of the 



^® Vulpian, as quoted by Prof, 

 ^aivre, ' La Variabilite des Especes,' 

 i868, p. 112. 



20 Dr. P. Hoy, ' The American Natu- 

 ralist,' Sept. 1871, p. 579. 



2^ Dr. Giinther, in Owen's ' Ana- 

 tomy of Vertebrates,' vol. i., 1866, p. 

 667. Spallanzani has made similar 

 observations. 



22 A thrush was exhibited before 

 ^he British Association at Hull, in 

 1853, which had lost its tarsus, and 



this member, it was asserted, had 

 been thrice reproduced ; having been 

 lost, I presume, each time by disease. 

 Sir J. Paget informs me that he feels 

 some doubt about the facts recorded 

 b}'^ Sir J. Simpson (' Monthly Journal 

 of Medical Science,' Edinburgh, 1848, 

 new series, vol. ii. p. 890) of the re- 

 growth of limbs in the womb in the 

 case of man. 



23 ' Atti della Soc. Ital. di Sc. Nat.,' 

 vol. xi., 1869, p. 493. 



