EUDIMENTARY ORGANS. 289 



struggle for life. In other wingless insects the want of 

 wings has been advantageous for other reasons. Viewed 

 by itself, the loss of wings is a degeneration, but in these 

 special conditions of life it is advantageous to the organism 

 in the struggle for life. 



Among other rudimentary organs I may here, by way of 

 example, further mention the lungs of serpents and serpent- 

 like lizards. All vertebrate animals possessing lungs, such 

 as amphibious animals, reptiles, birds, and mammals, have a 

 pair of lungs, a right and a left one. But in cases where the 

 body is exceedingly thin and elongated, as in serpents and 

 serpent-like lizards, there is no room for the one lung by the 

 side of the other, and it is an evident advantage to the 

 mechanism of respiration if only one lung is developed. A 

 single large lung here accomplishes more than two small ones 

 side by side would do ; and consequently, in these animals, we 

 invariably find only the right or only the left lung fully 

 developed. The other is completely aborted, although existing 

 as a useless rudiment. In like manner, in all birds the right 

 ovary is aborted and without function ; only the left one is 

 developed, and yields all the eggs. 



I mentioned in the first chapter that man also possesses 

 such useless and superfluous rudimentary organs, and I 

 specified as such the muscles which move the ears. Another 

 of them is the rudiment of the tail which man possesses in 

 his 3 — 5 tail vertebrae, and which, in the human embryo, 

 stands out prominently during the first two months of its 

 development (compare Plates II. and III.). It afterwards 

 becomes completely hidden. The rudimentary little tail of 

 man is an irrefutable proof of the fact that he is descended 

 from tailed ancestors. In woman the tail is generally 



