286 PLANKTON STUDIES IN RELATION TO 



which the one converged into the other, forming, so to speak, a mixed 

 sample. In one stomach only there occurred a pure zooplankton sample, 

 consisting almost entirely of Tcmora longicornis ; three other species 

 of Copepods were observed in extreme scarcity, viz. Centropages typicus, 

 Paracalanus parvus, Pseicdocalanus elongatus, together with a few Caridid 

 larvse and Amphipod remains. This sample alone constituted the one 

 extreme ; the other, which may be considered as phytoplankton, was 

 represented by three slight samples, which were composed mainly of 

 a number of plankton diatoms {Lauderia horcalis and Chaetoceras 

 dcnsum principally), together with a few bottom forms such as 

 Bhahdonema sp., forming with an indeterminable quantity of Phceocystis 

 glohosa a glutinous mass. Entangled in this material were observed 

 also a few Temora longicornis and the three other species of Copepods 

 above mentioned, together with a large number of Oikopleura dioica. 



In the case of the two mixed samples, two slightly different types of 

 food were observed. In the one Temora longicornis occurred fairly plenti- 

 fully throughout the stomach contents, which otherwise were composed 

 of the phytoplankton mass, as already described. In the second instance 

 Temora longicornis formed an almost pure sample in a layer deposited 

 above the phytoplankton. In connection with Oikoplevra dioica it is 

 interesting to note the following points. It occurred in greater abun- 

 dance in the stomach samples showing phytoplankton and mixed 

 material than it did in the tow-nettings taken from the Oithona (see 

 Table No. II, Sample No. 38). Secondly, it Vt^as not observed at all in 

 the sample composed entirely of Temora longicornis ; and lastly in the 

 mixed sample already referred to, where Temora was deposited in a 

 layer, it did not occur amongst the Copepod material, but was plentiful 

 in the lower layer of phytoplankton. These points alone in connection 

 with Oikopleiira dioica appear to constitute the sole difference existing 

 between the plankton samples and stomach material. 



CONCLUSION. 



It has been suggested by several previous authors* that the migra- 

 tions of the mackerel are not so extensive as hitherto generally 

 supposed. Cligny, in the paper already referred to, states that, as far 

 as his observations extend, mackerel return year after year, at 

 the close of the shoaling season, to certain confined areas not far 



* Allen, "Report on the Present State of Knowledge of the Habits and Migrations of 

 Mackerel" {Scomber scomhcr), p. 26, M.B.A. Journal, vol, v. (N.S.). 



Garstang, " On the Variation Races and Migrations of the Mackerel " [Scomhcr 

 scomhcr), p. 286, ihid. 



Cligny, Les pr6tenclues migrations du Maquereau, 



