EFFECT OF CROWDING ON SURVIVAL 187 



The longer tests were terminated piecemeal, as different individ- 

 uals fragmented their arms to such an extent that comparisons were 

 no longer fair. The records show the rate of oxygen consumption, as 

 well as the total oxygen consumption, of twelve groups of aggregated 

 Opliiodcrma during their entire starvation period, and of six lots of 

 similar size and number which had been isolated until they, too, died 

 of starvation and confinement. In addition to the corrections for 

 the slight difference in amount of water available for each animal, 

 the crude data were further corrected for differences in weight, since 

 tests had shown that, within the size limits used, oxygen consump- 

 tion is directly related to the size of the animal, although the greatest 

 observed spread between the total weight of 8 isolated animals and 

 either of the accompanying bunches was only 0.4 gm. 



Six tests were run to determine the initial relations in oxygen con- 

 sumption of isolated and bunched individuals. When these were 

 examined at the end of the first 4 hours, it was found that on the 

 average the groups of larger individuals, totaling 48 in all, had con- 

 sumed 208 cu. mm. of oxygen per individual of 1.25 gm. moist 

 weight. The 48 smaller animals making up the second bunch had 

 consumed 197 cu. mm. when reduced to the same standard weight; 

 while the 48 isolated starfishes had consumed 379 cu. mm. per stand- 

 ard individual of 1.25 gm. Here we see again that at the start of the 

 experiment the isolated individuals are consuming oxygen at a much 

 higher rate than are their aggregated fellows when the only known 

 difference between them is that the latter have been allowed to col- 

 lect in bunches. When these results are examined statistically by 

 Student's method, we find that there are 66 chances in 10,000 of 

 random sampling yielding such a wide deviation from the mean. 

 Needless to say, such results are statistically significant. This initial 

 relationship continued in most cases past the first 12 hours, and 

 sometimes past the 24-hour samphng, but had usually disappeared 

 before 48 hours. 



Two of these initial sets of experiments and four other similar 

 ones were followed through with starving animals until terminated 

 by death or by fragmentation of the arms. The mean results in 

 terms of total oxygen consumption of the surviving members of each 



