526 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



small. Especially careful collections were made in this lake and in the neighboring 

 waters and in sufficient numbers to give a good idea of its flora and fauna. 



There are no natural lakes in the Canal Zone; the Canal Commission, however, has 

 built for salutary purposes a series of reservoirs and these, having been in existence for 

 a considerable period, may be considered as lakes. Only the following three yielded 

 Rotatoria in any considerable number: Rio Grande, built in 1906, elevation 240 feet, 

 depth 50 feet; Camacho, built in 1907, elevation 370 feet, depth 45 feet; and Carabali 

 or Gorgona, built in 1906, elevation 76 feet, depth 10 feet. While the Rio Grande is 

 considered as constructed in 1906, it is really an old French reservoir which was built 

 some time between 1882 and 1889 and has had a continuous existence since that time; 

 it covers an area of 72.77 acres. 



These reservoirs were made by constructing dams in places where the waters of small 

 streams could be impounded. The beds were cleared and after construction the shores 

 were kept clear of vegetation to a distance of 50 or more feet from the margin. The 

 reserve ii-s were all "plankton-jwor." This is what would be expected from the 

 environment, which produces permanent bottom stagnation. In cold climates the 

 bottom waters of lakes have a more or less complete stagnation in the summer and in 

 winter, the stagnation being more complete in the smaller bodies of water in which 

 winds have no opportunity to produce bottom currents, but in spring and in fall, 

 because of the change in temperature, there is a complete overturning of the water. 

 No such change, of course, takes place under the constant temperature conditions of 

 the Canal Zone, so that only the surface water contains the oxygen which is necessary 

 for the life of plankton organisms. While the foregoing statement is true in regard to 

 the general conditions of the waters of the reservoirs, it must not be understood aa 

 meaning literally that the oxygen content always diminishes in exact ratio to the 

 depth; local and meteorological causes may produce some modifications of the general 

 statement. This has been discussed by Downes, who gives a series of charts of dis- 

 solved oxygen.^ 



For preserving the collections two different mixtures of alcohol and 

 forraahn solution were used by Doctor Marsh, one of equal parts of 50 

 per cent alcohol and 5 pei* cent formalin, another of equal parts of 75 

 per cent alcohol and 5 per cent formalin. In the matter of producing 

 recognizable material of the illoricate species of Rotatoria they are 

 on the same footing; only narcotizing will do that. But an alcoholic 

 mixture is far better for the subsequent sorting out of the material, 

 which necessarily contains a certain amount of plant debris; if a 

 straight formalin solution is used, this debris sticks to the animals so 

 that it is almost impossible to clean them. An alcoholic preservative, 

 on the contrary, leaves everything free and it is a comparatively 

 simple matter to pick out the animals. The strength of the alcohol 

 does not appear to be very important; probably 75 per cent alcohol 

 is as good as any. 



To facilitate reference the localities yielding large collections of 

 Rotatoria are numbered as below and the number added in parenthesis 

 after the record of each species. 



1. From the railroad bridge over water in Black Swamp; now 

 submerged in Gatun Lake. 



1 Downes, J. R., A study of the water supplies of the Isthmus of Tanama. Proc. Canal Zone Med. Ass., 

 Mount Hope, C. Z., vol. 3, pp. 133-150, 7 pis. 



