312 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



On looking over the remaining plankton hauls which 

 are not vertical, but which are for the most part surface 

 and horizontal, some taken with smaller and some with 

 larger nets, there is no doubt that the outstanding 

 character of the collection is the profusion of large 

 Calanoid Copepoda. We came upon them in our first 

 hauls in the Sound of Mull on July 12th, and they were 

 also abundant outside Mull, at Tiree, off Hyskeir, off 

 Eigg, around Skye, at the Shiant Isles, and the Ascribs, 

 off South Rona and Raasay, up Loch Torridon and the 

 Gi-airloch on the mainland, and in Loch Hourn and the 

 Sound of Sleat off Isle Ornsay, and finally as far South 

 as the sea between Colonsay and Islay, and as late as the 

 end of August. In most of these localities Calanus 

 finmarchieus was present in abundance, and also Pseudo- 

 calanus elongatus. Other abundant Copepoda are Acartia 

 clausi, Temora longicornis and Oiihona similis, sometimes 

 Centropages hamatus, and usually large numbers of 

 Copepod nauplii; but in all the cases of a really large 

 gathering of macro-plankton, such as those shown in 

 fig. 1, the conspicuous feature is the great abundance 

 of Calanus finmarchieus. The three collecting jars seen 

 along with the large Hansen net (diameter of mouth = 

 1 metre) contained catches of 1,700 c.c, 1,000 c.c, and 

 900 c.c. respectively, which consisted very largely of 

 Calanus finmarchieus. The number of individuals present 

 in the largest haul we have estimated to be about half-a- 

 million.* 



*As an example of the reliance that may be placed upon the relation 

 between volumes and counts when dealing with such an organism as 

 Calanus in plankton, it may be recorded that Professors Newstead and 

 Herdman, when on board the yacht, counted the individuals in 8 c.c. of 

 the plankton in the fresh condition on the evening it was taken, and 

 found that quantity to contain 2,400 specimens of Calanus. The gathering 

 taken from the same swarm a few days later, and amounting to 1,700 c.c, 

 has now been estimated independently by Mr. Biddell, in the laboratory, 

 as the result of the counting of several samples, to contain " fully half-a- 

 million specimens of Calanus." On the basis of the count at Tobermory the 

 large gathering would come out at 510,000 — practically the same as Mr. 

 Eiddell's result. 



