76 Proceedings of the Hoi/al Irish Academy. 



proved incorrect. As this question, however, is still being investigated, it will 

 not be discussed here except in so far as our observations on Lough Neagh 

 are concerned. The Copepods and Daphnids are most certainly feeding 

 upon the phytoplankton, upon Diatoifis and smaller green flagellates, most of 

 which are not captured by the net (in the same way as one of us has shown 

 the marine Copepoda feed). Now as this phytoplankton is extremely 

 abundant, we should expect the zooplankton and other animal dependents 

 to be also very abundant. This is strikingly the case ; and at the top of the 

 scale we have the phenomenal abundance of the famous Pollan. The food 

 of this fish will be discussed below. 



At the same time, if organic carbon compounds are found in solution, 

 there is no doubt that in many cases they will be made use of by aquatic 

 animals. Though no analyses for organic carbon have been made on Lough 

 Neagh water, we would suggest, from the quantities of phytoplankton, that 

 all the conditions for a large quantity of organic carbon in solution are to be 

 found, and that no doubt the water of the lake is just as abundant in detritus 

 and organic carbon in solution as could possibly be expected for a lake of this 

 size unless abnormally contaminated with organic matter. 



"Water-bloom" has occurred on two occasions. One of the most 

 extraordinary " water-blooms " was that caused by Gomphosphaeria Naegeliana 

 in September and November. This blue-green alga is exti-emely prolific in 

 Lough Neagh and occurs frequently all through the year. On November 11th 

 it was present in an extraordinary amount, and formed a compact layer on 

 the surface of the water. Now this alga differs from all others we have dealt 

 with in marine or fresh water in a curious way which has not been noticed 

 before so far as we are aware. It always rises to the surface of the lake 

 if the water is undisturbed, and this buoyancy is a character which, unlike 

 that of all our other planktonic organisms, is retained after fixation and 

 preservation. In our tubes of plankton, containing 5 per cent, formalin, 

 which have stood for two and a half years and have been shaken up at 

 intervals, the plankton forms the normal layer at the bottom of the tube, 

 with, however, another layer at the surface of the liquid. Thus it is impossible 

 to estimate the volume of the catch by allowing it to settle, for part 

 " settles upwards " and the rest downward. The material at the surface is 

 entirely composed of one form. Thus in our catches it is possible to 

 remove completely all the Gomphosphaeria by simply taking off the surface 

 layer. 



If the catch is transferred to 75 per cent, spirit, the alga falls to the bottom 

 on standing like the other constituents, and thus the remarkable difference 

 in buoyancy is not observed. 



