432 
the water was then covered with a mixture of paraffine and beeswax. The 
animals in the jar where the stems protruded through the seal invariably 
lived longer. The periods for the beetles were about 1 and 3 days re- 
spectively. 
Light—The pord is fairly well lighted throughout its entire depth 
during the day except when it is covered with snow. The light is reduced 
considerably by the growth of Typha. WKofoid (04) feund that, with the 
development of phanerogams in one of the backwater ponds tributary to 
the Illinois River, there was a marked reduction in the plankton. Some 
comparative observations were made on a pond about five miles west of 
this one. It has about the same area and depth but there is no Typha 
growing in it. Although no quantitative methods were applied, cladocera, 
copepoda, and chlorophyceze were much more in evidence in it during Sep- 
tember, 09, than in the pond under discussion. It seems probable that the 
reduction of the light by the Typha growth has resulted in fewer species 
and individuals developing in this pond. 
On Jan. 11, 1909, the ice was partially melted. Openings had formed 
in the ice avound the ‘Typha stems and about 23 to 3 inches of water stood 
above the remaining ice sheet. Cyclops was quite abundant in this upper 
layer of water which was certainly due to their being phototactic. It was 
the only organism detected. <A lowering of the temperature under such 
conditions would certainly destroy many individuals. Thus an adaptation 
presumed to be beneficial under one condition becomes destructive under 
certain other conditions. 
Food Relations.—Regarding the nutrition of aquatic organisms there 
are two theories, which, although not mutually exclusive, are essentially 
different. 
The older oue is that the ultimate source of feod is chlorophyl bearing 
plants and the various forms ot bacteria which produce nitrates and nl- 
trites. ‘The materials thus elaborated or their derivatives are ingested mts 
food vacuoles, gastrovascular spaces, or alimentary tracts of animals, where 
they are acted on by secretions of the animal, reduced to a solution and 
absorbed. This theory has been assumed by most zodlogists in their dis- 
cussions of food relations, and it is the most fundamental assumption in 
the investigations now being prosecuted by the International Fishery Or- 
ganization. 
