1855.] Development of Animal Life if t Time. 83 



mata,) we find two extinct ordinal types only, tlie J'rilobita and the 

 Cystidece. 



Among the Mollusca there is absolutely no extinct ordinal type ; 

 nor among the Radiata (Actinozoa and Hydrozoa) ; nor is there 

 any among the Protozoa. 



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

 tion 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 ugain, 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 living forms in time, in fact, is admitted by 

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

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

 the other that it is for the present undiscovered. 



According 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 its falling in with the 

 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 develop- 

 ment is not through the forms of the lower, but through forms 

 which are common to both lower and higher : a fish, for instance, 

 deviating as widely from the common Vertebrate plan as a 

 mammal. 



The Progression theory, however, after all, resolves itself very 

 nearly into a question of the structure of fish-tails. If, in fact, we 

 enumerate the oldest known undoubted animal remains, we find 

 them to be Graptolites, Lingulce, Phyllopoda, Trilobites, and 

 Cartilaginotis fishes. 



The Graptolites, whether we regard 'them os Hydrozoa, Anthozoa,' 

 or Polyzoa, (and the recent discoveries of Mr. Logan would strongly 

 favour the opinion that they belong to the last division,) are cer- 

 tainly in no respect embryonic forms. Nor have any traces of 

 Spongiadce or Foraminifera (creatures unquestionably far below 

 them in organization,) been yet found in the same or contem|)o- 



