90 



frequently discharged from the body which as a rule is not 

 done with important organs. The same thing holds true for 

 the so called Cuv'erian organs, situated in their immediate 

 neighborhood, the function of which is as yet unknown except 

 for their importance as organs of defence. For these organs 

 Mines 85 and 86), has shown that their discharge takes place 

 simply by an increased internal pressure, not by any intrinsic 

 action of the tubes themselves. 



Winter stein has studied the relative importance of the 

 water-lungs in the gaseous exchange. He estimated the exchange 

 in normal conditions and also when the water-lungs are put 

 out of commission by means of a rubber condom, using 

 Winkler's method for the estimation of O. : 50 / of the 

 total respiratory exchange appears to go through the lungs. 

 The fore-gut and tentacles play no important role, as similar 

 experiments in which the head was covered, show. 



Crozier 19) has calculated the amount of water pumped 

 through by the large Bermudian species, Stichopus moebii. 

 This was done by determining the amount of water pumped 

 through in one pumping and figuring out the average number 

 of pumpings in one day. 



He concludes that 20' 21 L. is pumped through per day 

 by a large Stichopus 24.5 c.M. in length. Compared with 

 the figures for some other animals this is fairly low. In 

 the sponge Spinosella Parker 97) found, that by a single 

 ,,finger" as much as 78 L. a day is pumped through, and for 

 Ascidia atra Hecht 52) found as much as 173 L. a day. This, 

 however, is not strange if we remember that in these animals 

 the watercurrent has the double function of carrying oxygen 

 and food, whereas in Holothurians only the oxygen is needed. 



1. In this big species Crozier found a difference in PH between 

 coelomic and sea water, (contrary to my findings in the starfish, mentioned 

 in the chapter on the perivisceral fluid) due to CO.? of course. The 

 PH of sea water is 8.2 ; that of the perivisceral fluid is 7.6. The water 

 expelled during spouting has a PH = 7.8; this shows: 1. that actually 

 respiration takes place through the lungs, 2. that the short stay of the 

 water in the lung is sufficient for the respiratory exchange. 



2. Frequently small fishes are found in the cloaca of large Holo- 

 thurian species, f.i. Fierasfer in the cloaca of Holothuria. 



Summarising these remarks on the organs of respiration in 

 Echinoderms, we may quote the words of D e 1 a g e and 

 Herouard: ,,L'animaI respire par tous les points ou une 

 membrane mince separe les liquides de 1'economie d'une eau 

 de mer plus ou moins renouvelee". 



b. Are there catalases and peroxydases 

 in the perivisceral fluid. 



We must in the first place try to get some information 

 ' as to whether the perivisceral fluid may be considered as a medium 



