OF GREAT BRITAIN. 23 



tually on their backs, unless artificially supported. 

 This support they seek to obtain by placing them- 

 selves amongst gravel or in crevices between 

 stones, exhibiting generally a great desire to escape 

 observation an instinct given to them no doubt 

 for their preservation during so feeble and helpless 

 a condition. On the disappearance, however, of 

 the yolk-bag they come from their hiding-places, 

 and are to be found, on careful search, in the 

 gentler eddies and small back-waters of the streams 

 in or near which the old Salmon had deposited 

 their spawn during the preceding winter. 



At two months old the Parr begins to acquire a 

 more symmetrical form, and the disproportion in 

 the size of the head ceases to be observable ; at 

 four months the characteristic Parr-marks are 

 clearly defined, and at six months the fry has 

 reached the length of from three to four inches, 

 and is the small-sized Parr so constantly found in 

 salmon-rivers. Extraordinary variations, however, 

 are discovered in the growth-rate of fish of similar 

 ages and even belonging to the same brood a fact 

 not hitherto entirely satisfactorily explained ; and, 

 within certain limits, the fish of different rivers 

 also vary in this manner not only in size, but often 

 in shape and colour, as much as do the qualities of 

 the streams themselves. 



