AGGREGATIONS OF HIGHER ANIMALS Ql 



from the beginning would be a long and laborious 

 series of experiments concerning the effects of num- 

 bers present upon growth. 



As long ago as the eighteen-fifties Jabez Hogg, 

 (62) an Englishman, found by experimenting that 

 crowding decreased the rate of growth of snails and 

 produced stunted adults. From that day to this there 

 has been almost no break in the reported evidence 

 that overcrowding reduces growth; the number of 

 reports that crowding in any degree increases growth 

 are relatively few. 



This phenomenon has, however, been observed by 

 enough workers using animals widely distributed 

 through the animal kingdom to show that the retard- 

 ing effect of undercrowding on growth is real. Before 

 considering the implications of this statement let me 

 review briefly some of the evidence. (3) Here as else- 

 where I shall make no attempt to catalogue all the 

 available evidence; the list would be impressively 

 long but tedious. 



It is relatively easy to show that mixed populations 

 of many animals grow faster than if the same number 

 of some one species are cultured together. The com- 

 mon experience of aquarium enthusiasts that the 

 presence of the snails in aquaria increases the rate of 

 growth and well-being of their fishes is a case in 

 point. Their rule-of-thumb experience has been fully 



