194 



Part III. — Seventeenth Annual Report 



The Daphnice of Loch Achray. (Plate VII., figures 22, 53.) 



Loch Achra}^, as already stated, receives most of its supply of water 

 from Loch Katrine, and probably the Daphnice found in it have been 

 introduced with the water from that loch. They belong to the same 

 species, but exhibit, perhaps, somewhat greater variation. It is interest- 

 ing to note that the Daphnice of Loch Vennachar — which receives the 

 overflow water from Loch Achray— appear to belong to Daphnia galeata. 

 Though hundreds of specimens from each of the three lochs — Loch 

 Katrine, Loch Achray, and Loch Vennachar — have been examined, none 

 were observed that could satisfactorily be ascribed to any other species 

 than the one named. This circumstance seems to favour the opinion that 

 the Loch Arklet and Loch Lomond Daphnice are but forms of the one 

 species — viz., of Daphnia laeustris. 



A few male Daphnice were observed in the Loch Achray gatherings, 

 and one of them is represented by figure 22. 



The Daphnice of Forfar Loch. (Plate VII., figures 23-28, 49.) 



In this loch the Dap/mice, which were very plentiful, appeared all to 

 belong to the one species — D. laeustris. A considerable proportion of 

 the young were furnished with a tooth on or near the top of the head, 

 as shown by figure 24 ; while the usual form of the adult females con- 

 tained in the different gatherings is that represented by figure 23. A 

 certain amount of variation was observed. This variation included a 

 slight difference in the form of the head and in the length of the posterior 

 spine ; figures 25, 26, and 27 represent a few of these differences. The 

 specimen represented by figure 26 has a very short posterior spine; while 

 in that represented by figure 27 the spine is obsolete. It will also be 

 observed that figures 25 and 26 are ephippial females which possess a 

 distinct bulge at the base of the posterior spine — a feature which is said 

 to be characteristic of Daphnia longispina. Moreover, the usual number 

 of preanal spines in the adult females is thirteen, but the number varies 

 in some specimens to twelve and fourteen ; the abdominal processes in 

 many of the specimens are also comparatively short (figure 49). In fact, 

 the Forfar Loch Daphniai possess characters which seem to indicate a 

 relationship with D. longispina, whilst others show as distinct an affinity to 

 D. laeustris. Figure 28 represents one of the male Daphnia: observed in 

 Forfar Loch. It has in many cases been noticed that the young Daphnia, 

 when about to leave the protection of the parent, has no tooth on the 

 head. A tooth appears, however, to be developed at a very early stage 

 in the growth of the specimens, and to be lost before maturity is reached. 

 No adults furnished with a tooth have been observed among the Forfar 

 Loch Daphnice) the tooth observed on the young was usually bidentate. 



The Loch Leven Daphniai. (Plate VII., figures 29-33.) 



Loch Leven is auother of the lochs recently examined in which 

 Daphnice are very abundant. In my paper on the invertebrates of this 

 loch (published in the Ninth Annual Report of the Fishery Board), I 

 ascribed the Loch Leven Daphnia to D. longispina, but they are now 

 referred to D. laeustris; it is really doubtful, however, if there is a single 

 character that can be laid hold of that is not, under varying conditions, 

 common to both. After the examination of many hundreds of specimens 

 there is only one mark which may be considered as belonging to D. 

 laeustris — viz., the presence in the young of a tooth on or near the top of 



