396 G. E. BULLEN. 



pointed out, appear to be solely on feeding migration. Moreover, in 

 all of the early spring " hooked " mackerel that the writer has 

 examined, the walls of the stomach have been of fair thickness. 



The evidence before us is certainly insufficient to warrant an 

 assertion that a physiological change is brought about in the nature of 

 the stomach by reason of a change of diet, but tlie fact remains 

 that the writer has found it possible invariably to determine the 

 general nature of the food contained in the stomach of a mackerel or a 

 pilchard from an external examination of the organ itself, before it is 

 opened. 



With reference to the transitional stage from the one type of feed- 

 ing to the other, the following note, received in the autumn of 1911 

 from Mr. Mathias Dunn, of Newlyn, is of considerable interest. This 

 observer states : — 



" I sent you yesterday some specimens of a rare Crustacean Macreypsis, 

 which has been very abundant on our coasts this summer. The mackerel 

 have been feeding ravenously on these animals, and at times have 

 pursued them into the harbour, where they have been so numerous as 

 to appear like thick porridge. We have had some excellent opportuni- 

 ties of seeing mackerel feed, during the visit of these little creatures. 

 They have been hunting up and down the back of the pier, like a pack 

 of hounds, going the whole length, turning and returning again and 

 again. They were swimming about ten to twelve feet off the pier in 

 company with a number of scads, about twenty to thirty in each shoal, 

 the scads in every case swimming close to the pier and the mackerel 

 just outside. The mackerel were swimming in open order, closing in, 

 rising and falling in graceful undulations, by which means they either 

 drove their prey on to the surface, where there was no escape, or 

 turned it to the centre of the shoal, where it was also promptly 

 despatched." 



Upon examination, the sample sent by Mr. Dunn was found to con- 

 sist almost entirely of the Mysid Crustacean 3Iac7-opsis stahheri, Van 

 Beneden,* together with a few young Herring (surface-swimming stage), 

 and a slight number of fish ova and the Copepod Centropciges typicus, 

 Kroyer. 



Unfortunately no stomach material was examined, but the foregoing 

 observations tend to show amongst other things that the fish 

 were feeding by sight, and were exercising discrimination in the 

 selection of their prey. At the time when these observations were 



* For the determiuation of this species the writer is indebted to Mr, W. M. Tattersall, 

 M.Sc. 



