RUDIMENTARY 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 
VOL. I. U 
