DEVELOPMENT OF ANIMAL LIFE IN TIME 301 



the enormous lapse of time of which we possess authentic records, the 

 extinct ordinal types are exceeding!}- few, and more than half of them 

 belong to the same class — Rcptilia. 



The extinct ordinal Reptilian types are those of the Pachypoda, 

 Pterodactyla, Enaliosmtria, and Labyrinthodonta ; nor are Ave at present 

 acquainted with any other extinct order of Vertebrata. Among the 

 Annulosa (including in this division the Echinoderinatd), we find two 

 extinct ordinal types only, the Trilobita and the Cystidece. 



Among the Mollusca there is absolutely no extinct ordinal type ; 

 nor among the Radiata {Actinosoa and Hydrozod) ; nor is there any 

 among the Protozoa. 



The naturalist who takes a wide view of fossil forms, in connection 

 with existing life, can hardly recognise in these results anything but 

 strong evidence in favour of the belief that a general uniformity has 

 prevailed among the operations of Nature, through all time of which 

 we have any record. 



Nevertheless, whatever the amount of the difference, and however 

 one may be inclined to estimate its value, there is no doubt that the 

 living beings of the past differed from those of the present period ; 

 and again, that those of each great epoch have differed from those 

 which preceded, and from those which followed them. That there 

 has been a succession of li\ing forms in time, in fact, is admitted by 

 all ; but to the inquiry — What is the law of that succession ? different 

 answers are given ; one school affirming that the law is known, the 

 other that it is for the present undiscovered. 



xA.ccording to the affirmative doctrine, commonly called the theory 

 of Progressive Development, the history of life, as a whole, in the past, 

 is analogous to the history of each individual life in the present ; and 

 as the law of progress of every living creature now is from a less 

 perfect to a more perfect, from a less complex to a more complex 

 state — so the law of progress of living nature in the past was of the 

 same nature ; and the earlier forms of life were less complex, more 

 embryonic, than the later. In the general mind this theory finds 

 ready acceptance, from the falling in with its popular notion, that 

 one of the lower animals, e.g. a fish, is a higher one, e.g. a mammal, 

 arrested in development ; that it is, as it were, less trouble to make a 

 fish than a mammal. But the speaker pointed out the extreme 

 fallacy of this notion ; the real law of development being, that the 

 progress of a higher animal in development is not through the forms 

 of the lower, but through forms which are common to both \o\<j&c and 

 higher : a fish, for instance, deviating as widely from the common 

 Vertebrate plan as a mammal. 



