306 THE OLDEST AIR-BREATHERS 



Crusoe. We see five fingers and toes, and ask how this 

 numerical arrangement started at once from fin rays of fishes 

 all over the world ; and how it has continued unchanged till 

 now, when it forms the basis of our decimal arithmetic. 



Again, our reptiles of the coal do not constitute a continuous 

 series, and belong to a great number of distinct genera and 

 families, nor is it possible that they can all, except at widely 

 different times, have originated from the same source. It 

 either happened, for some unknown reason, that many kinds of 

 fishes put on the reptilian guise in the same period, or else the 

 vast lapse of ages required for the production of a reptile from 

 a fish must be indefinitely increased for the production of many 

 dissimilar reptiles from each other ; or, on the other hand, we 

 must suppose that the limit between the fish and reptile being 

 once overpassed, a facility for comparatively rapid changes 

 became the property of the latter. Either supposition would, 

 I think, contradict such facts bearing on the subject as are 

 known to us. 



We commenced with supposing that the reptiles of the Coal 

 might possibly be the first of their family, but it is evident 

 from the above considerations, that on the doctrine of natural 

 selection, the number and variety of reptiles in this period 

 would imply that their predecessors in this form must have 

 existed from a time as early as any in which even fishes are 

 known to exist ; so that if we adopt any hypothesis of deriva- 

 tion, it would probably be necessary to have recourse to that 

 which supposes at particular periods a sudden and as yet un- 

 accountable transmutation of one form into another ; a view 

 which, in its remoteness from anything included under ordinary 

 natural laws, does not materially differ from that currently re- 

 ceived idea of creative intervention, with which, in so far as 

 our coal reptiles can inform us, we are for the present satisfied. 



There is one other point which strikes the naturalist in con- 

 sidering these animals, and which has a certain bearing on such 



