EVOLUTION AND DEGENERATION OF ORGANS 29 



In an adult cell, adaptation may, in a more or 

 less normal way, cause the formation of new organs. 



Even completely specialized cells of an organism 

 may, when placed under certain conditions of life, 

 adapt themselves to those new conditions and give 

 rise to successive generations of different cells, thus 

 generating other kinds of organs than those to 

 which they would have given birth under normal 

 conditions. This happens, for instance, with all the 

 cells of Salix, which are capable of reproducing the 

 whole organism by means of budding. This organic 

 plasticity is shared with the Begonia Rex, but in that 

 case it is only thoroughly developed in the epidermic 

 cells. Analogous examples abound among animals, 

 especially in the lower zoological groups. 1 



1 Loeb has shown that in certain groups, when the organism, 

 after having been wounded, is subjected to unusual light, position, 

 or pressure, organs are formed at the wounded part, which are 

 essentially different from those which would have been formed 

 in a normal recovery. When this heteromorphosis occurs in 

 Tubularia mesembryanthemum, Aglaophenia pluma, AntJiennu- 

 laria rosa, etc., the positions of the oral and apical poles may 

 be transposed. When Antennularia is placed so that gravity 

 acts upon it in a contrary direction to the ordinary one, there 

 are formed oral and apical branches, where they would not have 

 been formed had the organism been kept in a normal position. 

 (Jacques Loeb, Unters. zur physiol. Morplwlogie der Thiere : I. 

 Ueber HeteromorpJwse, Wiirzburg, 1891 ; II. Organbildung und 

 Wachsthum, Wiirzburg, 1892.) 



Similarly there is a true heteromorphosis when in a case of 

 club-foot the faces and articular surfaces of the bones and 

 cartilages assume characters adapted to the new work thrown 

 on them as the abnormality of the joint increases. Another 

 such case is in the false joints sometimes formed when the two 



