374 CHAPTERS ON EVOLUTION. 



' ; embryonic " fossil forms represent the early and lower phases in 

 the development of the species. The animal of to-day represents 

 the cumulative advance of its race. It forms a striking confirmation 

 of the evolution theory that we should discover in the debris of past 

 epochs, and in the lower life of these epochs the actual evidences of 

 such advance. The conception of the evolutionist that the 

 development of life is represented by a huge tree with its innumer- 

 able diverging branches and twigs, is thus seen to fit the actual 

 details of which his theory takes cognisance. The species of to-day 

 represent the topmost or last developed leaves of the branches. 

 Occasionally, we are able to trace the continuity of past and present 

 along the branch and backwards to the stem. And even where this 

 continuity is broken, it is interesting to note how the evidences of its 

 former existence became clear, when, in the shape of the lower and 

 earlier fossils, we behold the scars and lopped branches, showing the 

 lines wherein the development of the past had progressed. 



The imperfection of the geological record has already formed 

 the subject of a previous discussion. We traced the absence of 

 many of the connecting links between existing groups of animals to 

 the non-preservation of the forms of the past, as well as to the 

 wholesale destruction of fossil-histories which changes to the rock 

 masses undoubtedly involved. Despite the effect of such sweep- 

 ing physical revolutions, the evidence for the existence of these 

 " links " between existent forms which evolution postulates, has 

 been shown in not a few cases to be singularly complete. It is 

 necessary, however, to refer more exactly in the present instance 

 to the actual causes which have rendered the fossil record, at the 

 best, of fragmentary nature. There are thus, firstly, certain groups 

 of animals which, from the very nature of their habits, we 

 could not expect to have been well represented by fossil species. 

 Such forms as insects and birds, for example, could rarely be 

 expected to become readily fossilised. Their habits lead them 

 to exist in the majority of cases far from water ; and the lightness of 

 their bodies would largely preclude the probability of their frequent 

 deposition amongst the debris of seas and lakes such deposition 

 being, of course, the natural prelude to their preservation as fossils. 

 The comparative scarcity of bird and insect fossils fully attests the 

 correctness of these deductions. What is true of these two groups 

 holds equally good in the case of most land animals. By far the 

 greater proportion of fossils consist of the remains of marine or 

 aquatic forms, which naturally exist in the most favourable situation 

 for becoming readily entombed in the soft deposits which form the 

 rock-formations of the future. Another important consideration 

 which has had a notable influence in demonstrating why we can 

 never hope to construct a full and complete history of the past 



