EVIDENCE FROM TAILS, LIMBS, &* LUNGS OF ANIMALS. 105 



possesses a tail-fin resembling the unequal tail seen permanently repre- 

 sented in the ganoid fishes of to-day (e.g. Sturgeon). The permanent 

 tail-fin appears almost like a second anal fin (Fig. 43, B) the anal 

 being the fin (Fig. 38, a) situated in the middle line of the fish below. 

 As the spine develops, it is formed behind around the bent-up end 

 of the notochord (Fig. 43, c); and as development is completed, the 

 perfect and still unequal tail-fin of the flounder appears under a sym- 

 metrical guise, from its encroaching upon and ultimately replacing 

 the primitive fin. It is a noteworthy fact that certain of the stages 

 exhibited by the tail of the flounder and of other fishes during de- 

 velopment, present, as already remarked, the closest possible likeness 

 to the permanent condition of the tail in some of those fishes in 

 which the tail is markedly unequal in form. 



After such revelations from the laboratory of the zoologist, we 

 may be prepared to discuss the validity of the conclusions to which 

 the evolutionist is led namely, that the unequal tail-fin is the 

 primitive form of that appendage, and that this tail, in its turn, was 

 preceded by a straight or rounded termination to the body, repre - 

 sented by the first stage of development in the flounder (Fig. 43) and 

 in other fishes. The history of the individual fish and its tail, in 

 other words, presents us with a short recapitulation of the evolution 

 of the whole fish race and the tails thereof. 



Such a speculation seems perfectly consistent with the facts of the 

 case, provided we admit that, as the scientific world is well agreed, 

 the development of an animal presents us with a panorama of its 

 descent. Regarded otherwise, the ever- varying and often inexplicable 

 succession of stages in animal development simply appear before 

 us as a collection of phenomena without any conceivable meaning 

 or interpretation. But if in the record of fish-development it 

 may be accepted as true firstly, that the unequal-lobed tails be- 

 long to the oldest members of the class ; and, secondly, that the 

 great bulk of our modern fishes with even tails are to be regarded as 

 being " foremost in the files of time," and relatively new-comers on 

 the stage of life it may be further asked if any counter-proof to these 

 assertions is capable of , / 



being produced. Fortu- 

 nately, in the science of 

 fossils we possess a 

 means for verifying and 

 substantiating our con- 

 clusions. Suppose that 

 we hark backwards in 

 time, and try to discover 



the exact succession and FlG - 4* IcLr. 



order in which the fishes have appeared, as indicated by their fossil 



