THE FRESH- WATER LOCHS OF SCOTLAND. 33 



most abundant. Cyclops, especially 6'. strenuus, was also. plentiful. 

 Ostracoda were not so common in the loch itself as they were around its 

 margin, particularly those parts that were more or less overgrown 

 with vegetation, as round the north-east shore. Seventeen species of 

 Ostracoda were obtained along this part of the shore; twelve species 

 were obtained from the south shore, and only eight from the loch itself. 

 Among the Cladocera the rare and interesting Leptodora Jiyalina 

 occurred in considerable numbers; Monospilus tenuirostris was also 

 frequent in tjie material collected at one or two places. The following 

 were the common species: Gammarus pulex, Diaptomus gracilis, 

 Cypria sertna, C. ophthalmica, Limnicythere sancti-patrici, Daphnia 

 lacustris, Phurorus triynntUu8 y Cliydorus sphcericus. 



The larvae of insects were abundant in the loch, especially the larvae 

 of the Iphemeridae. The Libellulidae and Phryganidae were also repre- 

 sented in the larval stage more or less frequently. Some idea may be 

 formed of the myriads of these organisms present in the loch when it is 

 stated that a conspicuous ridge composed of cast-off skins of insect larvae, 

 which had been washed ashore during the preceding stormy weather, 

 extended along the margin of the loch for a considerable distance. The 

 curious so-called " water-bears " (Tardigrada), now included in the 

 class Arachnida, were common among the decaying vegetable matter at 

 the bottom. Species of Notonectidae or " water-bugs," and of aquatic 

 Coleoptera were also more or less common, though their distribution 

 seemed to be more localised. 



The worms were represented by several species parasitic and non- 

 parasitic. Among the former were Schistoceplialus solid us, obtained 

 from the body -cavity of a Stickleback (Gasterosteus aculeatus), and a 

 species of tape-worm (Bothriocephalus latus?), several of which were 

 found in the alimentary canal of the trout, six specimens being taken 

 from one fish. The heads of the parasites were fixed at the extreme 

 end of the cceca or blind tubes of the stomach, and their bodies were 

 so elongated as to extend well down into the intestine. Uusally one 

 parasite occupied a ccecum. Tubifex rivulorum was very common in the 

 loch. 



Rhizopoda were common all over the loch. Several forms were 

 obtained in the dredged and hand-netted material; the more typical 

 varieties observed were: Difflugia pyriformis, D. globularis (much 

 less frequent than the first named), D. corona (appeared scarce), D. 

 marsupiformis (of frequent occurrence). Diatomacea were abundant, 

 especially in the deeper parts of the loch, and included a considerable 

 number of species. 



Mr. Scott visited Loch Leven again in September and December, 

 1897, and in March and June, 1898, when he found that the free- 

 swimming Entomostraca, though very abundant, consisted mainly of 

 the one species, Daphnia lacustris. Leptodora hyalina was moderately 



