RUDIMENTARY ORGANS OF ANIMALS 141 



to the same organ in the whole series of vertebrates. 

 In man the mesial part of the thyroid gland is 

 reduced, but it cannot correctly be said that the 

 organ itself is degenerating. The contrary may 

 even be asserted, for all we know upon the subject 

 goes to prove that in mammals the thyroid gland 

 is formed and established at the expense of the 

 primitive rudimentary organ of which all the 

 morphological and embryological connections are 

 changed. This secondary development, entailing 

 the loss of a reduced ancestral organ, is attended 

 by a functional modification of great importance. 

 The primitive function probably discharged by the 

 gland has given place to another and rather vague 

 function, but one which is connected with the 

 breaking down of toxic matter formed by living 

 tissues. 



An examination of the vertebrae of vertebrates 

 will show the existence of rudimentary organs 

 throughout the whole group, each type and each 

 individual among the vertebrates exhibiting special 

 degeneration. In order to briefly demonstrate this 

 point, take two quite different types of which all 

 the vertebrae are well known and can therefore 

 be examined without difficulty : man and the 

 frog. 



We know that the construction of the primitive 

 bony vertebra was as follows : a centrum, carrying 

 neurapophyses, an intercentrum, carrying haema- 

 pophyses, and a pair of unforked ribs. 



