424 



THE PINNA. 



his bag as fast as he can, and when his breath begins to fail, shakes his rope as a 

 signal, and is drawn up together with the bag. 



Very exaggerated accounts have been given of the time passed under water by the 

 divers, from two to seven minutes being mentioned as the usual periods. The real fact, 

 however, is, that one minute is the ordinary average ; a few men being able to endure 

 an immersion of a minute and a half. This is a long period, as any one will confess 

 who has attempted to repeat the feat. Yet, with a little practice, it can be achieved, 

 even by those who can lay no claim to extraordinary capacious lungs; and I have more 

 than once performed it with tolerable ease. If the lungs be thoroughly filled four or five 

 times in succession, and emptied to the last gasp, so as to expel all foul air that may 

 be lingering in the tiny vesicles, the blood becomes so well oxygenized, that a further 

 supply of breath will not be needed for some time, and a deep inspiration will serve to 

 keep the blood in a healthy state for a marvellously long time. All swimmers who are 

 fond of diving will find that they can remain under water nearly twice their usual time 

 by taking this simple precaution. 



PEARL OYSTER. Meleagriaa margarltlfera. 



The best plan for procuring the Pearl Oyster is evidently the employment of the 

 diving bell, so that the best shells might be leisurely selected, the spot left undisturbed, 

 and the sharks outwitted. In the illustration are given specimens of the shell in various 

 stages, as well as the interior, showing the pearls as they appear when the animal is 

 removed. 



REVERTING to the illustration on page 422, we see a large, flattish, wedge-shaped 

 shell lying on the rock, and moored to the stone by a number of short threads. This 

 is the PINNA, so called from the Latin word, signifying a wing. 



The aggregate mass of these threads is termed the byssus, and is, indeed, a very 

 curious object. The threads are spun by the foot, and are attached to the centre of each 

 valve, thus forming a powerful cable by which the shell is moored to the rock. The 

 threads are wonderfully strong, silken in their texture, and, had the mollusc been 

 sufficiently plentiful, might have been employed in various manufactures. In the British 



