ig2 



ANIMAL AGGREGATIONS 



the observed effects might be due to physical rather to chemical 

 factors, at least in this case. In other words, it seemed possible 

 that in the absence of suitable non-ophiurid materials the animals 

 might themselves serve as substitutes for certain elements of the 

 normal physical environment. 



This possibility was tested by placing glass rods of different 

 lengths, bent into different shapes, in some of the Erlenmeyer res- 

 piration flasks and using these for isolation chambers. The glass 



TABLE XV 



Showing the Initial Relations in Oxygen Consumption of Ophioderma Iso- 

 lated INTO Flasks Containing Irregular Heaps of Glass Rods, in Com- 

 parison WITH Bunched Individuals and with Those Isolated into Plain 

 Flasks 



(The Results Are in Terms of Cu. Mm. of Oxygen Consumed 

 per Mean Individual of 1.25 Gm. Weight) 



rods formed a loose irregular pile, over and through which the 

 starfish could crawl or against which it could come to rest. Four 

 such flasks, with their accompanying controls, were added to the 

 series already described. Such experiments were begun only after 

 the conclusions outlined above were clearly indicated; they com- 

 prised six sets of 4-hour tests of initial respiration and two of the 

 long-time respiration experiments. The tests were made similarly in 

 every respect to those already described ; the flasks containing glass 

 rods were placed alongside those with isolated and bunched indi- 

 viduals with the behavior of which they were to be compared. 



The results of exposure for 4 hours under these conditions are 

 shown in Table XV. Here the respiratory rate is calculated in 

 terms of 1.25 gm. per individual and for the actual amount of water 



