THE SALMON 35 



old parr, 5 to 9 inches long, in the British Museum 

 collection, differ from those described above in that 

 the maxillary extends to the vertical from the 

 posterior edge of the pupil and the pectoral fin is 

 shorter, not reaching the vertical from the origin of 

 the dorsal. 



Mr. Malloch has observed that in the winter 

 mxonths parr leave the shallows and rest under 

 stones ; he has often lifted a flat stone quietly and 

 has seen three or four parr, which did not swim 

 away for a time, but appeared dazed and sleepy. 



When they are about two years old, or a little 

 more, parr become very silvery, their parr-marks are 

 obscured, and they are known as smolts, the name 

 being derived from an old English word meaning 

 *' shining." This silvery appearance is doubtless 

 produced by the formation of iridocytes, granules or 

 plates of guanin, in the skin outside the scales. 

 The smolts drop clown the rivers, and on reaching 

 the estuaries appear to migrate rapidly right out to 

 the open sea. Although the majority of the smolts 

 are two years old, it is possible that some may be 

 only one, or that a few may be three years old. 

 On some Norwegian rivers the parr are said not to 

 change into smolts and migrate to the sea until 

 they have spent as many as five years in fresh water. 



The main descent of the smolts usually takes 

 place about May, but varies from March to July 

 in different seasons and on different rivers. Some- 

 times there is a second migration in the late summer 

 or autumn, but Mr. Malloch thinks that this is the 

 case only when the parr have made their way into 

 small streams, and a deficiency of water has kept 

 them back during the course of a dry summer. 



