12 



THE STORY OF FISH LIFE. 



have probably arisen by a modification of these 

 balancing organs. Poised in the water the fish 

 is free to move in all directions. To adapt the 

 fish still more perfectly to its environment a 

 very peculiar organ, known as the air-bladder, 



has been developed, 

 at least in the 

 majority of living 

 forms, as well as in 

 the more modern 

 fossil types. This 

 air-bladder seems to 

 render the specific 

 gravity of the fish 

 the same as that 

 of the surrounding 



FIG. 1. A. Common Roach, showing Water. Modifications 

 arrangement of fins, and general which theair-bkdder 

 shape of body. D. dorsal fin ; C. .,, , 



caudal or tail fin ; A. anal fin ; PI. may Undergo Will be 

 Pelvic or ventral fin ; P. pectoral ^ niin ^ nn Q lof ATT\QO-O 

 fin ; O. gill cover; L. lateral line ; IOUn< 



t. transverse line. The significance Further adapta- 

 of the transverse and latera 1 lines is . , , 



explained further on. Only a few tlOH tO aquatic needs 

 scales have been indicated, in order Vaq rp^nlr.prl in a 

 that the transverse and lateral lines " ' jCSUlted 

 may be rendered more conspicuous. Complete investment 

 B. An outline figure of the Bur- f ~]j mp . howronionq 

 bot (Lota vulgaris), for comparison OI f lime > noWCOplO 



this Secretion may 

 -i n r -n 



bream-tishers Will 



testify ! This slimy 

 coat reduces friction to a minimum. Beneath 

 this slime we can generally descry a series of 

 overlapping plates the scales ; these fit closely 

 one over the other so as to offer a perfectly 

 smooth surface. 



The fish, as we have just remarked, being 



with fig. ,4., note the difference in 

 the shape and position of the fins 

 and the absence of scales.-After 



GUnther - 



