CAN ORGANS REDEVELOP NEW FUNCTIONS ? 243 



SECTION I. 

 Rudimentary organs. 



1. Animals. In Birgus latro (a land-crab of the 

 Philippines), the gills are atrophied and the bronchial 

 chamber is very richly supplied with blood vessels, 

 while a kind of incipient lung is formed from the 

 lining membrane of the reduced bronchial chamber. 1 



However, it is by no means certain that the 

 atrophy of the bronchial apparatus has preceded 

 this development of a pulmonary apparatus. In 

 the following case it rather seems to be one in 

 which a rudimentary structure has redeveloped in 

 order to assume a new function. In the develop- 

 ment of the urinary organs, it appears that the 

 ducts of the mesonephros are quite independent of 

 those of the pronephros, although these mesonephric 

 ducts become functional later in the embryonic life 

 than the pronephric ducts. They are, neverthe- 

 less, formed at an earlier stage, and their rudiments 

 have appeared before there is any trace of the others. 

 From this fact it would appear that in some 

 ancestors of existing vertebrates there existed simul- 

 taneously mesonephric canaliculi and canals homo- 

 logous with them, but exercising a different function. 

 Such a condition actually exists in Amphioxus : in 

 the branchial region of that animal there are pro- 

 nephric urinary canals and genital chambers which 



1 Semper, "The Natural Conditions of Existence as they affect 

 Animal Life." (International Scientific Series.) 



