ants' nests. 357 



arrangement. I have noticed them in cherry trees and Paulownias. 



The smaller and very timid species of Colobopsis build them- 

 selves nests in the hardest wood. These nests open outward by 

 only a very few small apertures, which are concealed by the 

 irregularities of the bark of the tree. These apertures are kept 

 closed by the head of a " soldier " sentinel, who permits only 

 friends to enter. The soldier's head is broadened and rounded 

 off in front, evidently for this very use. The rounded surface 

 (front view in Fig. ii, magnified ten times) is rough, of a dull- 

 brown colour ; the feelers are planted back of the rounded surface, 

 so that the latter presents no hold and blocks up the entrance to 

 the nest like a living stopper. I first observed this fact among our 

 Colobopsis irimcata^ Spin, at Vaux, Canton Vaud (Fig. 13, drawn 

 four-thirds of the natural size) but the similar structure of the head 

 and the habit of living in trees, which characterise the other species 

 of Colobopsis^ lead us to infer that they live in the same way. 



Fig. 13 represents a portion of the original piece of a nest of 

 Colobopsis truncata, discovered by me in a very hard, dead bough 

 of a pear tree. B is the bark of the pear tree ; Ch is the cham- 

 bers and passages of the nest ; O is the exterior opening of the 

 nest ; behind it, in the gallery of egress of the nest, stands a 

 Colobopsis " soldier " as a sentinel, keeping 'the door closed with 

 his head. At W are seen two Colobopsis workers, one hastening 

 toward the door from the outside, the other standing in the nest. 

 The soldier will go back into the nest for a moment in order to let 

 the first worker come in (I have noticed this among the living 

 ants). That the part played by the Colobopsis " soldier " is that of 

 a living stopper is further proved by the fact that there are com- 

 paratively few of them, and that in contrast to the workers they 

 hardly ever go out. Fig. 19 represents a "soldier," still more 

 magnified, standing at the door of egress. 



Those species of Campojwtus which live in a similar way — 

 such as Camponotiis fnarginatus, Latr. — display the beginning of a 

 similar rounded surface on the front part of the head, and always 

 have a large-headed sentry at the door. 



Leptothorax acervorum, F., cuts small, very simple nests, spread 

 out flat, with few chambers in the outer layer (tlie cork layer) of 

 the bark of the tree. Fig. 5 represents such a nest two-thirds of 

 the natural size in the bark of a fir. 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. VII. z 



