188 THE STORY OF FISH LIFE. 



in the mud for the purposes of concealment. To 

 this adaptation is due the peculiar and familiar 

 elongated form. This change in shape has been 

 followed by the loss of the pelvic fin in all, and 

 both the pectoral and pelvic fins in the mursenas, 

 whilst the scales have been reduced to mere 

 vestiges embedded in the skin. Moreover, the 

 primitive condition of a continuous median fin 

 fold, from the middle of the back to the middle 

 of the belly, has once again been introduced, 

 or secondarily acquired, as it is scientifically 

 expressed. Eeasoning from experience, some 

 scientific specialists in the natural history of 

 fishes, have been led to suspect that the supposed 

 common descent of these three forms of eels may 

 prove to have no foundation in fact. In other 

 words, that originally unlike and uni-elated forms 

 have become moulded by adaptation into a 

 common resemblance. 



Fossil eels occur in the upper cretaceous rocks 

 of Mount Lebanon. The eels form a sub-order 

 by themselves at present — the Apodes. 



Near here we encounter a host of familiar 

 forms, constituting the sub-order, Pledospondyl% 

 of Dr Smith Woodward. This sub-order em- 

 braces the carps, breams, roach, chubb, barbel, 

 gudgeon, tench and loaches. 



These are forms with which we are all more 

 or less familiar: a comparatively modern group 

 of fishes, carrying us back but a very little way 

 into the past, geologically speaking. 



So it is with the cat-fishes, which are generally 

 regarded as a tribe which may claim kinship 

 with the above. In the record of the rocks we 



