ATROPHY OF ORGANS FROM TRANSFERENCE 269 



become rudimentary in later stages on account of 

 their functions being assumed by other organs. 



(1) Atrophy of the tail in Batrachia Anura, and 

 of the larval gills in some insects. The tadpole of 

 the frog has a well-developed tail which acts as 

 the organ of locomotion ; the adult animal moves 

 by its limbs, and the tail, useless in the adult, has 

 been removed by phagocytosis. 



The aquatic larvee of many terrestrial insects 

 possess tracheal gills, that i to say, membranous 

 expansions of the skin, within which tracheae 

 ramify. In the adult insect respiration is con- 

 ducted by normal trachea? communicating with the 

 air, and the larval organs of respiration atrophy. 



In addition to such cases of atrophy occurring 

 normally in the life-history of individuals, there 

 are known many cases where the organs of a 

 species have disappeared on account of the trans- 

 ference of their functions. 



(2) Disappearance of limbs. Vertebrates which 

 move by general undulations of the body have 

 lost their limbs for this reason. Such cases are 

 Slow-worms, Amphisbsena, Snakes, Eels and Cae- 

 cilians. 



Many parasitic creatures have similarly lost their 

 organs of progression, as they depend upon their 

 host for movement from place to place. 



Sacculina, a parasite on the carapace of crabs, 

 has completely lost its organs of locomotion. More- 

 over, as it takes its food by processes passing into 



