NATURAL HISTORY OF CREATION. 147 



the lung structure either makes no advance at all, or 

 only appears in the rudimentary form of an air-bladder. 

 So, also, the baleen of the whale and the teeth of tlu> 

 land mammalia are different organs. The whale, in 

 embryo, shows the rudiments of teeth ; but these, not 

 being wanted, are not developed, and tlie baleen is 

 brought forward instead. The land animals, we may 

 also be sure, have the rudiments of baleen in their 

 organisation. In many instances, a pai-ticular structure 

 is found advanced to a certain point in a particular set 

 of animals (for instance, feet in the serpent tribe), al- 

 though it is not there required in any degree ; but the 

 peculiarity, being carried a little farther forward, is 

 perhaps useful in the next set of animals in the scale. 

 Such are called rudimentary organs. With this class of 

 phenomena are to be ranked the useless mamma' of the 

 male human being, and the unrequired process of bone 

 in the male opossum, which is needed in the female for 

 supporting her pouch. Such curious features are most 

 conspicuous in animals which form links between various 

 classes. 



As formerly stated, the marsupials, standing at the 

 bottom of the mammalia, show theii- affinity to the 

 oviparous vertebrata, by the rudiments of two canals 

 passing from near the anus to the external surfaces of 

 the viscera, whicli are fully developed in fishes, being 

 required by them for the respiration of aerated waters, 

 but which are not needed by the atmosphere-breathing 

 marsupials. We have also the peculiar form of, the 

 sternum and rib-bones of the lizards represented in the 

 mammalia in certain white cartilaginous lines traceable 

 among their abdominal muscles. The struthionid^e 

 (birds of the ostrich type) form a link between birds and 

 mammalia, and in them we find the wings imperfectly or 



