108 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Megalopa 



6 



1 



Zoea 



59 



10 



" Mysis " 



110 



18 



Podon 



4 



1 



Calanus 



30 



5 



Pseudocalanus 



200 



33 



Temora 



1,300 



217 



Centropages 



12 



2 



Anomalocera 



9 



1-5 



Acartia 



310 



52 



Oithona 



120 



20 



Oikopleura 



4,300 



717 



Only perfect specimens of Oikopleura were counted. It is 

 quite certain that the figures given do not nearly represent the 

 true numbers eaten by the six fish. The stomach contents 

 were very much digested, and it was quite obvious that the 

 Oikopleura had suffered more in the process than the other 

 organisms. The heads had become separated from the tails 

 in very many cases. There were numerous muscle fibres 

 present from the broken-down stomach walls which without 

 careful examination, by staining, dehydrating and mounting 

 could be easily mistaken for the tails of Oikopleura. Detached 

 tails and heads were therefore not taken into account. The 

 numbers given are an extremely low estimate of what were 

 actually consumed. 



On the same day the mackerel were caught Professor 

 Herdman had taken five hauls with the coarse and fine nets 

 in the same area where the fish were found. These enable us 

 to compare the numbers of Crustacea and Oikopleura in the 

 plankton through which the fish were swimming with the actual 

 contents of the stomachs. The total volume of the five hauls 

 was 47 cubic centimetres. The mean number of copepoda 

 present in each haul was practically 47,000 specimens, of which 

 34,000 were Oithona. Two species of copepoda present in 

 the plankton hauls were not observed in the stomach contents. 



