THE VEGETABLE AND ANIMAL KINGDOMS. 127 



which it flies : in the extinct pterodactyle, the same purpose 

 was chiefly served by a development of the fifth finger alone. 

 The fundamental resemblance which lurks below various ap- 

 pearances is often startling. Thus, the giraffe, with its long 

 neck, has, in that part, no more bones than are to be found in 

 the neck of the elephant and pig, which hardly seem to have a 

 neck at all. The cervical vertebrae are but seven in every one 

 of the mammalian animals. Sometimes, an organ appears 

 entirely wanting in one family, as feet in the serpent tribes, a 

 pelvic region in the whale, the wing in the bird called the 

 apteryx ; and yet it is not truly wanting. Usually, some 

 rudiment of it appears, as if nature had been willing to give it, 

 but had kept it back from a complete development, as know- 

 ing it to be not needed in that instance. On this ground, the 

 notion of a much ridiculed philosopher of the last century, re- 

 specting a human tail, may be said to be not quite without 

 foundation. Between the fifth and sixth week a tail exists in 

 the human embryo ; it then goes back ; but still in the mature 

 subject its elements are seen clumped up in the bone at the 

 bottom of the spine, the os coccygis. 



Unity of organization becomes the more remarkable when 

 we observe that the corresponding organs of animals, while pre- 

 serving a resemblance, are sometimes put to different uses. 

 For example, the ribs become, in the serpent, organs of loco- 

 motion ; and the snout is extended, in the elephant, into an 

 instrument serving all the usual purposes of an arm and hand. 



It is equally remarkable that there should be, in the original 

 plan of the animal structure, a double set of organs, one or 

 other of which is selected for development according to the 

 needs of the particular animal. Thus there are in the plan 

 both gills and lungs, two wholly distinct kinds of respiratory 

 apparatus, the one being designed for a watery and the other 

 for an atmospheric medium. The mammalia, as creatures 

 destined to breathe the air, are furnished with lungs ; but, at 

 an early stage of the foetal progress, this is not the case. They 

 have at that time a branchial apparatus. Afterwards, this goes 

 back, and the lungs are developed from a different portion of 

 the organism. Lungs, on the other hand, are possessed by 

 certain fishes in a rudimental form ; it is the well-known air- 

 bladder of those fishes, which are understood to profit by it, as 

 an additional means of floating. So, also, the baleen of the 

 whale and the teeth of the land mammifer are different organs. 

 The whale, in embryo, shows the rudiments of teeth ; but, not 



