PROGRESS IN BIOLOGICAL INQUIRIES, 1936 57 
effluents and soil constituents the manuscript for the second part of 
the pollution series studies, Trade Wastes, Chemical Effluents, and 
Natural Pollutants, has been prepared and will be submitted for 
publication during 1937. 
One of the striking findings in the investigations of natural pol- 
lutants has been the high toxicity of minute quantities of selenium to 
fish, as little as 0.05 mg. of selenium being sufficient to produce a 
peculiar “pop-eye” condition in catfish.after some 7 days. This con- 
dition was usually fatal in less than 3 weeks and was attended with 
marked edema and other pathological changes of the internal 
organs. This work on selenium is particularly significant in view of 
recent surveys which show this element to be a widespread menace 
in several Western States. 
Several other substances also found in sma!l quantities in some 
natural waters and soils, as boron, fluorides, titanium, etc., have also 
been found to present previously unrecognized hazards to fish and 
other aquatic life. 
The investigations on fish physiology as related to water conditions 
have been greatly extended during the past year with the perfection 
of new apparatus for studying fish respiration, heart action, and 
internal metabolic activities. 
MUSSEL PROPAGATION 
During the summer of 1936 approximately 40 million fresh-water 
mussels, about equally divided between the yellow sand shell, Lamp- 
silis anodontoides, and the river mucket, Actinonaias carinata, were 
planted at definite stations in northern Arkansas where the success 
of these stockings can be followed for the next 5 years. A good 
supply of brood stock for the river mucket has been located and 
during the spring of 1937 it is anticipated that the plantings listed 
above will be doubled. 
At Fort Worth, Tex., the long-time experiments on mussels in con- 
fined areas have been continued with satisfactory returns. These 
tests have confirmed the previous findings that the river mucket is 
the most promising species studied thus far for commercial propa- 
gation, and have given additional information on the survival of 
fresh-water mussels under adverse conditions. 
ICHTHYOLOGICAL INVESTIGATIONS 
DEVELOPMENT AND RATE OF GROWTH OF FISHES 
The study of a collection of young fishes from the South Atlantic 
States, principally from Beaufort, N.C., was continued by Dr. Samuel 
F. Hildebrand, assisted by Louella E. Cable. A manuscript devoted to 
the description of the development of 17 teleosts from the egg to the 
adult, as far as material was available, was prepared and submitted 
for publication. The rate of growth during the first year for some of 
the species is shown, and other life history notes and data are included. 
SURVEY OF THE FRESH WATERS OF MISSISSIPPI 
The general survey of fresh-water fishes in the State of Mississippi, 
undertaken by Dr. Hildebrand in 1933, was continued in cooperation 
