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Part III. — Seventeenth Annual Repwt 



merely expansions of the river. Now, reasoning by analogy, one would 

 be inclined to presume that the Daphnice of these Glen Garry lochs would 

 very likely belong to the same species as those of Loch Oich and Loch 

 Ness — and we have no reason to suppose that they are not the same 

 species. I am aware that some specimens of Daphnia which the Rev. 

 A. M. Norman collected in Loch Garry have been ascribed to a different 

 genus and species (Hyalodaphnia kahlbergensis, Schoedler) ; but Dr. 

 Brady, while so far recognising this identification, refers to the characters 

 relied upon for the discrimination of this form as being " very doubtful," 

 and adds : " Some of the helmeted forms — as, for instance, D. galeata — 

 have always a small, though distinct, eye-spot, but are in other respects so 

 closely similar to D. Imhlbergensis as to be with difficulty distinguished. 

 Under these circumstances Schcedler's generic name seems of questionable 

 value, and it may even be doubted whether all the members of the 

 helmeted group should not be looked upon as mere varieties of one very 

 protean species." Had Loch Garry been entirely separated from Loch 

 Oich (as Lough Erne is from Melvin Lough in Ireland, whence some 

 helmeted specimens have been sent to Professor Brady), there would have 

 been more reasonableness in the supposition that the Daphnice of the two 

 lochs were more or less distinct. However, seeing that a considerable 

 stream of water passes through Loch Garry, and after a course of a few 

 miles falls into Loch Oich, and also that Daphnice are decidedly pelagic 

 in their habits, and therefore liable to be transported from one loch to 

 another — especially when lochs and rivers are in flood — it will be of con- 

 siderable interest if it can be satisfactorily proved that a species of 

 Daphnia exists in this small Glen Garry loch distinctly different from 

 that observed in Loch Oich. I am rather inclined to think that if a 

 large series of the Loch Garry specimens were examined, as has been 

 done in the case of Loch Oich, they would be found to be specifically 

 identical with those of that loch. 



But the more interesting points in any discussion on the Daphnice of 

 these lochs are not so much questions as to whether certain modifications 

 should be regarded as being of specific or non-specific value, for the great 

 tendency to variation exhibited by this particular group of organisms is 

 so great, scarcely any of the several characters that have at one time or 

 another been selected as affording a means for discriminating between the 

 different forms can be relied upon as satisfactory; hence what may be 

 regarded as a species or a variety is, in not a few cases, simply a matter 

 of opinion. A more interesting point is the striking evidence which 

 these variations furnish of the apparent susceptibility of Daphnia} to the 

 influence of the changes that may occur in their environment. Another 

 point, and one which has already been touched upon, is whether the various 

 forms of Daphnia living in the same loch, or in a series of lochs of limited 

 extent and communicatiug directly the one with the other — as Loch 

 Katrine, Loch Achray, and Loch Vennachar — should all be considered 

 forms of one species ; or whether there is satisfactory proof that two 

 or more species of Daphnia may be, or have been, obtained under such 

 conditions. It is possible that in the large fresh-water lakes of Conti- 

 nental Europe — lakes which, when compared with the lochs of Scotland, 

 might almost be denominated inland seas — more than one species of 

 Daphnia is to be found ; but in the examination of the Scottish fresh- 

 water lochs, which has now been carried on for several years, I have so 

 far obtained no satisfactory evidence to show that more than the one 

 species is to be found in the one loch, or in a series of lochs directly 

 connected with each other as in the example cited above. 



The figures of Daphnia on Plate IV. represent female specimens 



