236 



SCIENCE. 



[N. S. Vol. XIV. No. 346. 



writers, and in some cases carried so far 

 that the process of regeneration itself is 

 supposed to be accounted for by the liability 

 of the parts to injury. In order that it 

 may not appear that I have exaggerated 

 the widespread occurrence of this belief a 

 few examples may be cited. 



Eeaumur in 1742 pointed out that regen- 

 eration is especially characteristic of those 

 animals whose body is liable to be broken, 

 or, as in the earthworm, subject to the at- 

 tacks of enemies. Bonnet (1745) thought 

 that such a connection exists as has been 

 already stated, and that the animals that 

 possess the power of regeneration have 

 been endowed with germs set aside for this 

 very purpose. He further believed that 

 there would be in each animal that regener- 

 ates as many of these germs as the number 

 of times that it is liable to be injured dur- 

 ing its natural life. Darwin in his book on 

 ' Animals and Plants under Domestication ' 

 says : " In the case of those animals that 

 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 Professor 

 Lessona * that this capacity is generally a 

 localized and special one serving to replace 

 parts which are eminently liable to be lost 

 in each particular animal. The most strik- 

 ing case in favor of this view is that the 

 terrestrial salamander, according to Lessona, 

 can not reproduce lost parts, whilst another 



* Delage and Giard give Lessona ( 1869) the credit 

 for first stating that the phenomenon of regen- 

 eration is an adaptation to liability to injury ; but 

 Eeaumur fi.rst suggested this idea in 1742 and Bonnet 

 in 1745. Delage's interpretation, viz., that Lessona 

 ascribed this to a ' jrrevoyaiice de la nature ' has been 

 denied by Lessona's biographer, Camerano (' La Vita 

 di M. Lessona' Acad. B. d. Torino (2), XLV., 1896) 

 and by Giard (' Sur L'autotomie Parasitaire,' etc., 

 Compt. Eendus de Seances de la Socieie de Biologie, 

 May, 1897). 



species of the same genus, the aquatic sala- 

 mander, has extraordinary powers of re- 

 growth, as we have just seen; and this 

 animal is eminently liable to have its limbs, 

 tail, eyes and jaws bitten off by other 

 tritons." 



Lang, referring to the brittleness of the 

 tails of lizards, points out that this is a very 

 useful character, since the bird of prey that 

 has struck at a lizard gets hold of only the 

 last part of the animal to disappear under 

 cover ; the lizard escapes by breaking off 

 its tail. The brittleness of the tail is, 

 therefore, an adaptive character that has 

 become fixed by long inheritance. 



To this example may be added that of 

 certain land snails of the Philippine Islands. 

 The individuals of the genus helicarion live 

 on trees in damp forests, often in great 

 droves. They are \ery active, and creep 

 with unusual swiftness over the stems and 

 leaves of the trees. Semper has recorded 

 that all the species observed by him have 

 the remarkable power of breaking off the 

 tail (foot) close behind the shell, if the tail 

 is roughly grasped. A convulsive move- 

 ment is made until the tail comes off, and 

 the snail drops to the ground, where it is 

 concealed by the leaves. Semper adds that 

 in this way the snails often escaped from 

 him, and from his collectors, leaving noth- 

 ing behind but their tails. The tail is said 

 to be the most obvious part of the animal, 

 and it is assumed that this is, therefore, the 

 part that a reptile or bird would first at- 

 tack.* Lang states that in this case exter- 

 nal influences have produced an extraordi- 

 narily well developed sensitiveness in the 

 animal, so that it reacts to the external 

 stimulus by voluntarily throwing off the 

 tail. It would be, of course, of small ad- 

 vantage to be able to throw off the tail un- 



* Whether, having once failed in this way to obtain 

 the snail, the bird or lizard would not learn to make 

 a frontal attack is not stated. Or shall we assume 

 the tail is all that is wanted ? 



