ZOOLOGY, 



STRAY NOTES. ON THE PEAEL MUSSEL. 



By WILLIAM JAPP, F.S.A. 



( Concluded. ) 



THE favourite habitat of the pearl mussels is a smooth stream, 

 with a gravelly bottom. Their natural preference is to 

 burrow : and it has been found that where a piece of water has 

 been almost depopulated by too severe fishing, very soon a new 

 colony may be seen taking up the position, and studding the 

 bottom of the river in myriads. Such a gravelly bottom gives 

 also the favourite feeding ground of the mollusc. Though at 

 times they are obliged to take refuge in clay, on it they are much 

 poorer and leaner than on the gravel. They are able, like trout, 

 to adapt themselves in the colour, to that of the bottom on which 

 they live; so that, if the clay is blue the mussel becomes blue ; and 

 even the pearls in such mussels assume a bluish tint. They have 

 a great capacity for food ; and when in health and in a suitable 

 locality, they are often crammed with it. 



They are very conservative in their location : and it is believed 

 that if nothing disturbs them, they can be identified as occupying 

 the same upright position for thirty years or more. If by any 

 chance the trunk of a tree has become fixed across the bed of the 

 stream, so as to act like a croy, making the current less rapid, 

 mussels will soon occupy this sheltered spot, and will at once 

 burrow a couple of inches into the gravel, and will adapt them- 

 selves to the requirements of their surroundings. There are all 

 kinds and conditions of river-beds, just as there are all kinds 

 and conditions of soils on the earth's surface ; and mussels like 

 the monks of old, soon find out and take possession of the most 

 eligible sites. The Isla bottom is richer than the Tay. The Tay 

 mussel is of the same variety as that from Balquhidder, though 



