TRANSFORMISM 211 



establish a host of logical relations between animals 

 of all kinds. 



It would show us a number of groups of animals 

 separated from each other by morphological dissimi- 

 larities. But let us also consider all those animals which 

 lived m the past of the earth, and the remains of which 

 are found m the rocks as fossils. Including all the forms 

 of hte known to Paleontology, we should find that the 

 dissimilarities between the various groups would tend 

 to disappear. The gaps between existing Birds and 

 Reptiles, for instance, would become partially bridged. 

 Palaeontology would also supplement morphology in 

 another way. The study of the structure of animals 

 leads us to describe them as " higher " and " lower "— 

 higher in the sense of a greater complexity of structure. 

 Thus the body of a Carnivore is more complex than 

 that of a Fish, inasmuch as it possesses the homologues 

 of the truly piscine gills, but it also possesses a four- 

 chambered heart instead of a two-chambered one ; 

 and it possesses the mammalian lungs, diaphragm, and 

 placenta, structures which are not present in the Fish. 

 Now, so far as its imperfect materials go, palaeontology 

 shows us that the higher forms of life appeared on the 

 earth at a later date than did the lower forms. The 

 remains of Mammals, for instance, are first found in 

 rocks which are younger than (that is, they are super- 

 posed upon) those rocks in which Reptiles first appear ; 

 and so also Reptiles appear later in the rock series 

 than do Fishes. Palaeontology thus adds to the logical 

 order suggested by morphology a chronological order 

 of this nature : higher, or more complex forms of life 

 appeared at a later date in the history of the earth 

 than did lower or less complex ones. 



A parallel chronological sequence would also be 

 suggested by the results of embryology. This branch 



