392 ORGANIC GROWTH sec. 



mental organism, as we have otouucIs for assumino- it once 

 was.^ 



The same process repeats itself in tlie individual develop- 

 ment of the worm — in all these cases we have definitely 

 directed processes of growth, which can only be the result of 

 inheritance. 



The remarkable fact that in an animal thus divided organs, 

 and sometimes very complex organs, develop in the proper 

 positions, without any aid from the direct action of external 

 stimuli, requires to be illustrated by further examples before 

 I enter more minutely into its explanation. 



Everyone knows that when the tail of a lizard is cut off 

 another grows in its place — even Pliny dilates upon the fact. 

 Aristotle mentions its occurrence in salamanders and snakes. 

 But the recrescence of such a complex highly-evolved organ 

 as the eye of vertebrates is much more remarkable. Blumen- 

 bach recorded the occurrence of this recrescence as early as 

 the last century, first in newts,^ and afterwards in Batrachia^ 

 (according to Merkel it had previously been recorded by 

 Briihl). But this recrescence only takes place when some 

 remnants of the various layers of the eye are left in connec- 

 tion with the uninjured optic nerve.^ In Batrachia, according 

 to Blumenbach, the lower jaw is also reproduced. The legs 

 of newts, when renewed, grow again in the same way as when 

 they develop in the larva3.^ The spinal cord is also repro- 

 duced in Amphibia and reptiles, as, for instance, in tadpoles, 

 in newts, in Pleurodeles Waltlii — in the latter animal very 

 completely in five months. The spinal ganglia likewise are 

 renewed, apparently growing out from the spinal cord.^ That 



1 Cf. p. 62. 



- Blumenbach, Specimen physiologiae comparatae, 1787, p. 31. 



•^ Idem, Kleinere Schriften zur vergleichenden, Physiologie, 1800, p. 31. 



■* J. Ch. Eggers, Von cler Wiedererzeugung, Wiirzburg, 1821. 



^ Gotte, Ueher Entwicklung und Regeneration des Gliedmassenskelets der 

 Molche, Leipzig, 1879. 



^ P. Fraisse, Die Regeneration von Geweben u. Organen hei den Wirbelthieren, 



