302 SCOMBEROIDES. 



female, in the water, by the shape of its head ; that of the 

 former being abrupt, and almost perpendicular, thus — 



while the female's is more rounded, thus. 



Yours, &c. J. P. C. 



Certain it is that in the spring they make their 

 appearance in vast shoals, scarcely inferior, as it 

 regards numbers, to the herring — being many 

 miles in extent. From some cause not yet under- 

 stood, the common mackerel appears to be consti- 

 tutionally subject to a disease of the tunica con- 

 junctiva, the skin covering the eyes.* This mem- 

 brane seems to thicken, during the winter, to such 

 a degree, as apparently to obstruct the entrance 

 of the rays of light to the retina ; but as warm 



* Effects of lime upon fish. — As a barge laden with lime 

 was proceeding up the Ouse from Lewes, from some cause 

 or other, it sunk near Barcombe. The effect on the fish in 

 the river was instantly manifested ; hundreds rose to the sur- 

 face, and a great number were taken by hand. Pikes were 

 seen darting about in great agony; and most of the finny 

 tribe within a mile of the spot where the accident occurred, 

 were rendered blind from the burning nature of the lime. It 

 is calculated that some thousands of fish perished. 



