154 Papers from the Marine Biological Laboratory at Tortugas. 



A was found to be dead at the end of 1.5 hours, 5 in 3 hours, and C was 

 living after 15 hours, but dead in 24. In a control culture in which the 

 body-fluid of the original host was used in place of that of Toxopneustes, A 

 lived about 2 hours, B was still active at the end of 24, and Cdied somewhere 

 between 15 and 24. It will be seen, therefore, that^ and C are less affected 

 by the change than is B, which normally lives 10 to 20 times as long in the 

 body-fluid of its own host as in that of Toxopneustes. Unfortunately D 

 was not available at the time when this experiment was performed. The 

 converse of the above experiment, namely, the subjecting of parasites ob- 

 tained from Toxopneustes to the body-fluid of Diadema, was also tried with 

 similar results. In this case only D was available, it being the only one of 

 the four forms found in quantity in Toxopneustes. In the control culture 

 in which the body-fluid of their own host was used the animals were 

 normal after 15 hours; in the body-fluid of Diadema they were dead in 2 

 hours. 



The injurious effects of transferring the parasites to the body-fluid of 

 an animal other than their host are almost certainly not due to physical 

 (e. g., osmotic) differences between the body-fluids of the two animals, since 

 they may be transferred with impunity from either host to sea-water, the 

 body-fluid of sea-urchins having approximately the same osmotic properties 

 as the latter. Furthermore, in a number of experiments in which the con- 

 centration of the liquid surrounding the parasites was purposely suddenly 

 altered, the forms in question were shown to be quite resistant to changes of 

 this sort. It may be assumed, therefore, that chemical rather than physical 

 differences in the two body-fluids are responsible for the death of the 

 animals. It is rather interesting that different races of the same species 

 are found adapted to different hosts and apparently can not be suddenly 

 transferred from one to the other. Where adaptive characters such as 

 these are concerned, we can look for a considerable amount of variation 

 within the species. But in the case of non-adaptive characters, such as 

 some of those mentioned in the succeeding experiments (resistance to HgS, 

 H2SO4, etc.), it was found that the properties of form D, for example, were 

 practically the same whether it was obtained from Diadema or Toxopneustes, 

 and consequently that such characters are fairly constant for the species. 



LENGTH OF LIFE OF THE PARASITES AFTER THE DEATH OF THE HOST. 



If a dead Diadema, either opened or unopened, be covered with sea- 

 water and allowed to stand in a warm room, the number of parasites present 

 soon begins to diminish and after a variable time all disappear. Sometimes 

 in as short a time as 12 hours none are to be found, though in other cases 

 they may be active for 24 hours or more. In no instance, however, do they 

 seem to persist more than 30 hours at the room temperature of the Tortugas 

 laboratory (85° to 95° F.). They usually disappear in the order, D, A, C, B. 

 In one series of observations D was dead in 12 to 15 hours, A ina. little less 

 than 20, while C and B survived somewhat over 24. While the absolute 



