342 C. H. TURNER. 



fourths of an inch ; the tunnels through the partition varied in 

 width from one half an inch to one half the length of the parti- 

 tion. The ants glued the partition to the roof in such a manner 

 that no matter how wide the tunnel, the felted roof always com- 

 pletely closed the crack. 



After the ants had begun to close the crack with the wall built 

 up within from the floor, the crack e was thereafter only imper- 

 fectly covered with trash ; furthermore, instead of covering the 

 edges b, c, d and / with trash, the same result was obtained by 

 chinking from inside the space between the glass cover and the 

 top of the walls of the brood chamber with material similar to that 

 with which they constructed the inner partition. 



To see if all colonies of Formica fusca var. subsericea Say would 

 behave in the same way in the presence of a crack across their 

 brood chamber, a crack was made in the top of the brood cham- 

 ber of each of four nests of this species. These nests were ob- 

 tained from the field and housed in Janet nests for this special 

 purpose. In two cases the ants with their young deserted the 

 chamber over which I had placed a crack and migrated to the 

 nest of another colony of the same species. 1 In one case the ants 

 with their young migrated from the compartment over which I 

 had placed a crack into another compartment of the same nest. 

 I forced them back into chamber C by substituting a piece of 

 colorless glass for the orange glass with which the chamber into 

 which they had migrated was covered. They and their young 

 remained thereafter in chamber C for six weeks without doing 

 anything that tended to close up that crack. In the fourth case 

 the ants with their young retreated from brood chamber C, over 

 which I had placed a crack, into chamber B. I then placed a 

 crack across chamber B and a complete cover over chamber C. 

 At once the ants covered the crack with trash but no partition 

 was constructed upon the inside. 



It is convenient to group the responses of animals living in 

 colonies into class responses and individualistic responses. A 

 class response is a stereotyped response which would be made by 

 any and each member of a group when confronted with similar 



1 The colony into which each of these colonies migrated contained, before the 

 arrival of the emigrants, no fertile females. 



