112 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



condition in July. Only three spent female fish and one mature 

 male were observed in 1913. The eggs were present in three 

 tow-nettings only in 1913. 



Food. 



The mackerel is a migratory pelagic fish and finds its 

 food in the water through which it swims. The food will, 

 therefore, vary according to the changes occurring in the 

 constituents of the plankton. An examination of the stomach 

 contents generally gives a fair indication of the nature of the 

 plankton in the area where the fish have been caught, especially 

 if they have been some little time in it. As the food consists of 

 the organisms in the water through which the fish swims, it 

 is to be expected that the fish in one area may be feeding on 

 quite a different kind of organism from those in another area. 

 It is well known that sudden invasions of organisms may occur 

 from time to time in the plankton, and may have quite a local 

 distribution. One of the most noteworthy of these sudden 

 invasions is the extraordinary shoals of the amphipod 

 Euthemisto compressa, which make their appearance along the 

 Yorkshire Coast occasionally in the spring, in such immense 

 numbers that drifts of them, several inches in depth, are thrown 

 up by the waves. The fishermen frequently remove the heaps 

 in barrow loads to put on their gardens as manure. This 

 amphipod is a distinctly northern form, and is usually regarded 

 as a rare species on the British coasts. Its occurrence in such 

 swarms so far from its true home has not yet been satisfactorily 

 explained. 



Dr. E. J. Allen gives a good account of the food of the 

 mackerel, and the method employed by the fish in procuring 

 it, in the Journal of the Marine Biological Association, N.S., 

 Vol. V. The smaller forms of plankton are collected by straining 

 the water through the gill-rakers as it swims along. Young 



