of the Fishery Board for Scotland. 



215 



the prevalent forms. Professor Cleve noted that the fronds of G. curvi- 

 setus were spore-bearing, — a fact which I had independently noted in this 

 species, as well as in G. borealis and G. constrictus. In addition to the 

 diatoms, and, as a rule, far exceeding them in total bulk, were the species 

 of Geratium. G Tripos, G. Fusus, and G. Furca were all three 

 present in nearly every haul of the nets, especially the first two 

 species. Sometimes one predominated, sometimes the other ; but, as a 

 general rule, C. Tripos prevailed in the Clyde sea-area, and G. Fusus in 

 the northern lochs, but never to the exclusion of the other. 



In December, on the west coast outside the Clyde sea-area, the 

 characteristic diatoms were Goscinodiscus concinnus, Biddulplda mobili- 

 ensis, Ditylum Briglitwellii, while species of Ckcetoceros and Navicula were 

 casually present. Both Geratium Tripos and G. Fusus appeared sparingly 

 in all the captures. Within the Clyde area, ISkeletonema became next 

 abundant to Goscinodiscus, after it Biddulplda, and next Ghcetoceros de- 

 cipiens, while Geratium Tripos and G. Fusus were more plentiful than in 

 the waters outside. Compared with these, other diatoms and plant 

 organisms were of purely casual occurrence. These appeared more or less 

 in every haul of the nets, and in fairly steady proportions, as cited. Not 

 a single specimen of Rhizosolenia was obtained in December, while some- 

 times in August it was the predominant generic form, e.g., in Kilbrennan 

 Sound. 



At all seasons of the year, especially near the shore, a small proportion 

 of the diatoms captured are dead, their cell-contents either disorganised or 

 gone. This is particularly noticeable in such large forms as Goscinodiscus 

 concinnus and Biddulphia mobiliensis ; but it occurs frequently in other 

 forms such as Glmtoceros decipiens, and, above all, in Skeletonema costatum. 

 I believe this phenomenon, which at first puzzled me greatly, to be due 

 to the decline or loss of salinity of the water. My reasons, for this belief 

 are these : Such diatoms are mostly found at or near the surface and in 

 the vicinity of land where a considerable mixture of fresh with salt water 

 occurs. This may be seen in any of our western sea lochs, especially after 

 rains, where a sheet of practically fresh water lies on the top very slowly 

 mixing with the salt water. It is well known that seaweeds, in general, 

 are extremely sensitive to variations in the degree of salinity. My belief 

 is strengthened by the following observation : In April, on ascending 

 Loch Fyne, the nearer we came to the top the larger the quantity of dead 

 diatoms were found. This was particularly noticeable in Skeletonema, 

 which almost monopolised the surface ; and on tow-netting in the waters 

 between Inveraray and Cairndhu at the head of the loch, where there was 

 a thick sheet of fresh water on the surface, owing to recent heavy rains, it 

 was impossible to find a living cell in the vast mass of Skeletonema. This 

 observation was confirmed in Loch Etive in summer. This loch was full 

 of Skeletonema, some at the surface, but most in from 3 to 5 fathoms. 

 A large quantity of fresh water was entering the loch, and the diatoms at 

 the surface were in large proportion dead, while those in the lower layers 

 were living. The observation is the more noteworthy, as I am led by 

 other reasons to think this diatom mostly abounds in waters of a fairly 

 low degree of salinity, and I have elsewhere taken the low degree of 

 salinity of this loch in August as possibly accounting for the presence of 

 Skeletonema in it at that season. However, this last idea is a purely 

 speculative one, and does not in any way affect my general contention that 

 the great numbers of dead diatoms in the sea are to be accounted for by 

 the addition of fresh waters. 



Diatoms as Food of Marine Animals. — When we reflect that the 

 whole bulk of animal life in the ocean must be dependent on the 



