PROGK.ESS IN BIOLOGICAL INQUIRIES, 1&24 39 



Quantitative studies of the bottom-dwelling animals showed that 

 the greatest rariety of forms inhabited the region over which the 

 depth of the water ranged from 1 to 10 meters, while the — 1 meter 

 zone was second in rank. The maximum number of individuals was 

 found in the 20 — 40 meter zone (6.765 per square meter), while the 

 minimum number was found in the — 7 meter zone (1,155 animals 

 per square meter) . Five groups of organisms constituted the main 

 element of the population in the deeper zones, namely, Nematoda, 

 Oligochaeta, Pontoj^oreia, Chironomus, and Tanytarsus. 



The weight of the bottom animals reached a maximum in the 

 20 — iO meter zone, namely, 155 pounds per acre, live weight (30 

 pounds, dry weight) : the minimum was found in the — ^1 meter 

 zone, 32 pounds per acre, live weight (7.8 pounds, dry weight). 



Tlie weight of the dry organic matter in the average standing 

 crop of plankton was a little more than 10 times as large as the dry 

 weight of the entire bottom population; thus the plankton feeders 

 among the latter have an abundant supply of food to draw upon at 

 all times. 



A 2-year study of the nitrogen compounds dissolved in lake 

 waters was completed in June, 1924. It was found that the total 

 soluble nitrogen in the surface water of Lake Mendota increases 

 during the winter months and decreases during spring and summer. 

 In the bottom water it increases in summer and in winter, or dur- 

 ing the two periods of stratification ; the minimum is reached dur- 

 ing the vernal and autumnal periods of circulation. The soluble 

 organic nitrogen, both in the surface and in the bottom water, 

 shows the same seasonal variations as the total soluble nitrogen. 

 Proteins, peptides, animo acids, and complex animo acid combina- 

 tions were found in solution in the various lake waters studied. 



FOULING or ships' BOTTOMS 



An investigation into the nature and extent of the fouling on 

 ships' bottoms was begun in September, 1922. This work is carried 

 on by Dr. J. P. Visscher, temporary assistant, in cooperation with 

 the Bureau of Construction and Repair of the Navy Department. 

 The object in view is to secure data that may be applied in prevent- 

 ing the attachment of the fouling organisms to the ships' bottoms, 

 which will show what conditions are most conducive to fouling, and 

 from which proper docking intervals for ships of various kinds and 

 with various histories may be determined. 



Examinations regarding the nature and extent of the fouling on 

 the bottoms of 175 vessels have been made since this investigation 

 was begun. Of these, more than 100 were made during the past 

 year, these representing approximately equal numbers of commercial 

 and naval craft. From these data the following conclusions can be 

 drawn : 



1. Fouling occurs almost entirely while vessels are in port. 



2. Vessels that are never in port for more than a few days at a 

 time, and whose next port of call is at a considerable distance, 

 rarely if ever accumulate much fouling. 



3. Fouling in north Atlantic waters is caused, in the order of their 

 importance, by barnacles, hydroids. algae, bryozoa. ascidians, and 

 by other growths of much less importance. 



