) 



of the Fishery Board for Scotland. 1 3 3 



INTRODUCTORY. 



In my paper oa the Invertebrate Fauna of the Inland Waters of 

 Scotland (published in Part III. of the Sixteenth Annual Report of the 

 Fishery Board for Scotland), it is stated in the preliminary remarks that, 

 at the request of the Fishery Board, a certain number of the fresh-water 

 lochs of Scotland were being examined at more or less regular intervals 

 in order that some information might be obtained concerning the effect 

 produced on the invertebrate fauna of these lochs by the changes inci- 

 dental to the different seasons of the year, and to discover whether 

 the various organisms living in the different lochs were, or were not, 

 equally susceptible to seasonal variation. 



This special work has now been completed, and a description of the 

 results obtained — so far as they relate to the crustacean inhabitants of 

 the various lochs examined — is embodied in the following pages. 



Before proceeding to give a description of the results, it will be 

 necessary to state briefly the names of the lochs examined, and the 

 method adopted in their examination. 



The lochs selected for special investigation were the following : — Forfar 

 Loch, near the town of Forfar ; Loch Leven, Kinross ; Loch Lomond 

 and Loch Katrine ; Loch Arklet, situated between Loch Lomond and 

 Loch Katrine ; Loch Achray, Trossachs ; Loch Doon, Ayrshire ; and 

 Duddingston Loch, near Edinburgh. Loch Lomond and Loch Katrine 

 are deep-water lochs ; Loch Arklet and Loch Doon are upland lochs, and 

 situated at a considerable elevation above sea level ; Forfar Loch, Loch 

 Leven, and Duddingston Loch are comparatively shallow lochs; Loch Achray 

 is a small loch, and seems to be merely an expansion of the River Teith, 

 which, issuing from the Trossachs end of Loch Katrine under the name 

 of Achray Water, spreads out into Loch Achray in its eastward course. 



These lochs were examined at intervals of about three months, and the 

 method adopted in their examination was somewhat as follows : — At a 

 suitable part of each loch tow-net gatherings were collected in the open 

 water by means of a rowing-boat. Two tow nets, made of silk and of 

 different degrees of fineness, were used ; the coarser one had about forty- 

 five meshes to the inch, which, when the net was wet, were sufficiently 

 close to capture very small entomostraca ; the other was much finer, having 

 at least four times as many meshes to the inch, and was used for the 

 collection of diatoms, infusoria, and similar minute organisms. Hauls 

 were made at various depths, but usually not below ten fathoms, as I 

 find from the examination of a considerable number of the lochs of Scot- 

 land that, with few exceptions, representatives of all the free-swimming 

 Entomostraca are to be obtained between the surface and ten fathoms. 

 These organisms appear to be distributed all through the water — at least 

 in the case of lochs that are shallow — and also to a considerable extent 

 where the water is of great depth — as in Loch Morar; generally, however, 

 it is found that under twenty or thirty fathoms the catches become smaller 

 the deeper the net is worked. Loch Lomond and Loch Katrine were 

 tow-netted at both the upper and lower ends. Along with the tow-net 

 work the temperature of the water, the direction of the wind, and the 

 state of the weather were recorded. In the case of the deep lochs three 

 temperature readings were taken — viz., at the surface, at five fathoms, and 

 at ten fathoms. In the case of shallow lochs, where the depth did not 

 exceed five or six fathoms, the temperature of surface and bottom only 

 was taken. Moreover, in addition to the tow-net work in the open 

 water, the shore, where suitable, w T as also examined by means of 

 a hand net (a small net mounted on a ring fixed to the end of a 



