OYSTER CULTURE IN GERMANY. 655 



muscles and cilia being weakened by the cold. Accord- 

 ingly, the oyster is no longer in a condition by means 

 of its rapidly-moving cilia, and the quick closing of the 

 valves of its shell, to drive out the particles of slime 

 brought in with the water. But the power of the cilia and 

 the elasticity of the muscles are again restored as the 

 water becomes warmer, providing the cold has not lasted 

 too long. The gills become clean once more, and respir- 

 ation and nourishment, which have been disturbed by the 

 sliming, proceed again as before. If the cold spell is 

 prolonged, then, in addition to the sliming of the gills and 

 mantle, there are yet other pernicious results. The shell- 

 muscle becomes so soft that it can no longer close the 

 valves. The cilia move slower and slower, and finally, 

 when the shell-muscle has allowed the valves of the shell 

 to gape wide open, cease moving altogether. The mantle 

 and gills become pale in colour, infusoria nest in them and 

 hasten their destruction, and soon their ciliated layer 

 separates and disappears. The softest portions of the 

 body, the generative organs, the liver, and the stomach 

 quickly vanish, probably consumed by snails, crabs, worms, 

 and star-fish as soon as they can make their way unhindered 

 into the open shell. The last part of the mollusc which 

 is to be found in the shell is the shell-muscle. It remains 

 free between the two valves, or attached to only one of 

 them, until finally but a trace of its fibres is to be seen 

 at the points of attachment, the so-called muscular impres- 

 sions. 



. . . . I have frozen the mantle and gill lobes of 

 oysters in North Sea water and allowed them to remain in- 

 closed in ice for an hour at a time, with the temperature of 

 the water varying in degree from 4 C. to 90 C. below zero. 

 When the ice had melted, the cilia began to move feebly, 



