SEA-FISHERIES LABORATORY. 157 



AN INTENSIVE STUDY OF THE MARINE PLANKTON 

 AROUND THE SOUTH END OF THE ISLE OF 

 MAN.— PART XIII. 



By W. A. Herdman, F.R.S., Andrew Scott, A.L.S., and 

 H. Mabel Lewis, B.A. 



Once again, from the pressure of other work, it has been 

 found impossible to undertake that general summary of our 

 accumulated data and re- consideration of our previous reports 

 which was promised. We can deal now, as before, only with 

 the observations and results of the past year — and these, 

 moreover, only in brief form in deference to the demand for 

 economy in printing. 



The work during 1920 was carried on in exactly the same 

 manner as in previous years, and 573 samples of plankton were 

 collected in the neighbourhood of Port Erin, and have since 

 been worked up in detail. These bring the total number of 

 samples for the 14 years' work, since 1907, up to 7,071. 



In addition to an average of six gatherings per week 

 throughout the year in Port Erin Bay, in the specially important 

 months of March, April, July, August and September special 

 hauls were taken both in the bay and outside in the open sea 

 from the motor-boat " Redwing." The results have been 

 treated in the usual way, and the forms, lists, tables and graphs 

 are stored available for future reference in the Oceanographic 

 Department of the University ; where also the accumulated 

 collections of plankton catches are housed. A special investi- 

 gation undertaken by one of us (W.A.H.) from the " Redwing " 

 on the variation observed in successive vertical hauls is dealt 

 with as a separate paper in this Report (p. 161). The folio whig 

 is only to be regarded as a summary of the outstanding facts 

 of the year 1920. 



The vernal plankton maximum was again in May, and the 



