1 84 ANIMAL AGGREGATIONS 



ference is large enough to be of significance. Student's method of 

 statistical evaluation shows that for all six experiments there are 49 

 chances in 1,000 of random sampling yielding so great a variation 

 from the mean in either direction. 



The one exception where the isolated individuals showed a greater 

 survival time is instructive. For some reason one or two of the ani- 

 mals in each of the bunches of this experiment died soon after one of 

 the daily inspections, disintegrated and polluted the whole liquid, 

 and caused the death of the remainder. Such an extreme catastro- 

 phe could not happen with the isolated individuals. 



The survival of the starfishes isolated into liter flasks containing 

 small heaps of variously bent glass rods is also instructive. Here the 

 starfishes came to rest on or among these glass rods just as in nature 

 they rest among eelgrass blades. It will be noted that for the two 

 tests made, the survival is comparable with that of grouped animals 

 rather than with the starfishes isolated into bare containers. It ap- 

 pears as though the satisfaction of the thigmotropic appetite has 

 approximately the same survival value whether the satisfaction 

 comes from contact with the piles of glass rods or the group of in- 

 dividuals of the same species. 



RESPIRATION STUDIES WITH ISOPODS 



The effect of aggregation upon the aggregants can be followed 

 more closely by studying the effect upon the rate of respiration. 

 Several such studies have been made with different animals, some of 

 which will be summarized. 



Preliminary experiments upon the two species of land isopods 

 mentioned above, indicated that soon after these isopods aggregate 

 their rate of respiration is decreased, as compared with similar ani- 

 mals isolated for a similar time (Allee, 1926). This tendency appears 

 after the isopods have been bunched for 5 minutes, and extends at 

 least through the first hour of bunching. When the bunches and 

 solitary individuals are compared after standing in the laboratory 

 for a longer period of time, the isopods taken at random from the 

 bunches are giving off carbon dioxide the more rapidly. 



Oxygen consumption of two other species of land isopods was 



