(if the Fixhrry Board for tfrntiand. 



199 



carrying pseudova or embryos, or which are developing ephippia, except 

 where otherwise stated. It is not pretended, however, that the specimens 

 are all equally mature. Dajphnice begin to bear pseudova at a compara- 

 tively early stage of development, and may, in the course of subsequent 

 stages, become altered in form ; they may develop larger abdominal 

 processes, and the number of preanal spines may be increased. All this 

 emphasises the need for extra carefulness, in dealing with such forms, not 

 to place undue value on characters so unstable as these are. 



As regards seasonal distribution, JJaphnia seems to be less affected by 

 the changes incidental to the different seasons than some of the other 

 entomostracan species appear to be. In the larger lochs the variation of 

 these organisms in regard to number was found to be usually very little 

 for the different seasons; and even in lochs of less dimensions — as Forfar 

 Loch, Loch Leven, and Duddingston Loch — the Daphnice, though some- 

 what less numerous in winter than in summer, were still comparatively 

 common. But while the distribution of Daphnia is fairly constant in 

 large sheets of water and even in lochs of moderate size, it is sometimes 

 different in the case of small bodies of water. In ponds, tarns, etc., 

 Daphnice occasionally exhibit some curious vagaries in regard to their 

 distribution. Prolonged dry or wet weather causes greater extremes in 

 the quantity of water present in such ponds and tarns than it does in the 

 larger lochs, and to this probably is due the erratic distribution referred 

 to.* The following is a brief narration of an example of this erratic dis- 

 tribution of Daphnia which last year came under my own observation. 

 Some time during the summer of last year I was informed by a friend that 

 Entomostraca were common in an artificial pond in the vicinity of Edin- 

 burgh. I visited the pond on 3rd July and found Daphnia pulex abundant. 

 Many of them were carrying psezidova, and males and ephippial females 

 were plentiful, but few other species were observed. On the 25th of 

 August following I made another visit to the same pond. The weather 

 during the interval had been dry and warm ; little or no rain had fallen, 

 and the quantity of water in the pond had become greatly reduced. It 

 might have been thought that in these circumstances the Entomostraca 

 would have become more crowded together and that a larger catch would 

 be obtainable than on the previous visit. The actual result was, however, 

 very different. It was found that Entomostraca were few, and that 

 Daphnia had entirely disappeared ; not a single specimen was obtained 

 though a more careful examination was made than on the former visit. 

 The interval between the two visits was seven weeks and three days. 

 This, however, can hardly be called an example of seasonal distribution. It 

 simply shows that in limited areas certain forms of Entomostraca may be 

 so affected by temporary physical changes as to cause, for a time at least, 

 their entire disappearance. 



Lyncodaphnid^] 



Lathonura redirostris, 0. F. Miiller. — This rare species was obtained 

 in two of the lochs examined — viz., Loch Doon and Loch Achray — but 

 it occurred in only one of the gatherings from each of these lochs. 



Streblocercus minutus, G. O. Sars. — The Dhu Loch (at the side of 

 Loch Lomond) was the only place where this rare Cladoceran was observed. 

 Only a few specimens have been obtained; but it is a very small species 

 and may readily be overlooked. 



* Such variations in the weather as described will occasion considerable changes in the 

 temperature of small bodies of water, and this also will have a certain influence bearing- 

 on the distribution uf the fauna and tlora. 



