12 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Copepoda alone. To take an example from the lower 

 marine plants : — In the Red Sea and on various occasions 

 in the Indian Ocean I have seen Trichodesmium 

 erythraeum forming a most conspicuous red-brown 

 or tawny yellow-brown scum on the surface of the sea for, 

 it might be, a few hundred yards up to a mile in width, 

 and several or even many miles in length, while the sea 

 at each side of the patch was entirely free from the 

 organism. Under these circumstances, and I believe 

 them to be the most usual circumstances, a sample taken 

 in the Trichodesmium area, or possibly two successive 

 samples taken by a vessel running along the length of the 

 tract, would give enormous numerical results, while if 

 the samples had been taken a mile away the conclusions 

 arrived at as to the prevalence and importance of the 

 organism might have been very different. Noctiluca 

 miliaris, again, is very local in its distribution. 

 Occasionally, during recent years, I have taken it in 

 abundance in late summer off the North Coast of 

 Anglesey, while Mr. Chadwick, tow-netting at the same 

 time at Port Erin, only 50 miles distant, across the same 

 sea, has not been able to find a single specimen. 



Before turning to my observations at Port Erin this 

 summer, let me direct attention to the results obtained by 

 Dr. Herbert Fowler in his expedition in the North 

 Atlantic in the summer of 1900 — a cruise which has 

 thrown much light upon the relations of oceanic plankton. 

 Dr. Fowler's results are very valuable in demonstrating 

 the varied composition of the plankton from day to day 

 in the open sea. His sixteen stations were so close 

 together that the whole area investigated measured only 

 66 miles by 22, and his results for the Chaetognatha show 

 that even at adjacent stations on successive days the 

 numbers obtained were very different, one catch being 



