406 L. H. HYMAN. 



In the experiments to be reported in this paper it was not my 

 purpose to make a complete study of the action of cyanide on 

 oxygen consrmption in these animals, since I had already done 

 that in the case of a sponge and Planaria, but merely to show 

 that cyanide in non-lethal doses reversibly decreases oxygen 

 intake. The experiments on the marine forms were performed 

 at the Marine Biological Laboratory, Woods Hole, Mass.; 

 those on the fresh-water forms at the University of Chicago. I 

 am greatly indebted to Professor F. R. Lillie for working space 

 at the first-named institution. 



The methods employed were identical with those used in 

 previous experiments on this subject and will be found described 

 in full in a former paper (Hyman, '19). Briefly, the animals 

 to be tested were placed in Erlenmeyer flasks or wide-mouthed 

 bottles of 500 to 600 c.c. capacity, these were filled air-tight with 

 water, and the animals allowed to respire in them for a con- 

 venient length of time. A sample was then withdrawn, and 

 this and a sample of the original water used were analyzed for 

 oxygen content by Winkler's method, the difference between the 

 two samples representing the oxygen consumed by the animals. 

 Two separate determinations of the oxygen consumption in 

 normal water were made, potassium cyanide was then added to 

 the water arid two more determinations in the presence of cyanide 

 carried out. The animals were then washed in several changes 

 of water, and their oxygen consumption in normal water tested 

 again a day or two later. Throughout each experiment, the 

 receptacles containing the animals were immersed in a water- 

 bath, the temperature of which was kept constant to 0.5 degrees. 



The possibility of iodine absorption by substances emanating 

 from the organisms was again considered, and was tested in the 

 case of two or three of the animals employed. Standard iodine 

 solution was added to water which had been standing on the 

 animals for at least one hour, and the iodine then titrated back 



half-grown individuals. It would thus appear that in these animals partheno- 

 genetic reproduction is accompanied by some degree of rejuvenescence. Green's 

 recent work on Simocephalus (BiOL. BULL., Aug., 1919) supports this suggestion, 

 since he found that these animals reproduce sexually early in ontogeny, and sub- 

 sequently the same individuals begin parthenogenetic reproduction, a reversal of 

 the order usually observed in parthenogenetic forms. 



