spatial Relatto?7S 331 



Station, that combines flying with water transportation. 

 Beavers swim with boughs for their dam, and w^ater- 

 striders run across the surface carrying their booty, but 

 here is a wasp that flies above the surface towing a load 

 too heavy to be carried. The freight is the body of a 

 huge black spider several times as large as the body of 

 the wasp. It is captured by the wasp in a waterside 

 hunting expedition, paralyzed by a sting adroitly 

 placed, and is to be used for provisioning her nest. 

 It could scarcely be dragged across the ground, clothed 

 as that is with the dense vegetation of the water- 

 side ; but the placid stream is an open highway. Out 

 onto the surface the wasp drags the huge limp black 

 carcass of the spider and, mounting into the air with her 

 engines going and her wings steadily buzzing, she sails 

 away across the water, trailing the spider and leaving 

 awake that is a miniature of that of a passing steamer. 

 She sails a direct and unerring course to the vicinity of 

 her burrow in the bank and brings her cargo ashore 

 at some nearby landing. She hauls it upon the bank 

 and then runs to her hole to see that all is ready. 

 Then she drags the spider up the bank and into her 

 burrow, having saved much time and energy by making 

 use of the open waterway. 



Intermediate between surface and bottom the life of 

 the water that is not included in either of the two strata 

 we have just been discussing, but that has continuous 

 free range of the open water, is still considerable. It 

 corresponds in part to the plancton of the open waters, 

 as we have seen. It corresponds in part, also, to the 

 necton; and, as in the open water, so also in the shoals, 

 the larger and more important free- swimming animals 

 are fishes. Its spatial relations are complicated by the 

 habit some air-breathing forms (especially insects) 

 have of ranging downward freely thro the depths; 



