THE INSURGENCE OF LIFE 137 



kittiwakes and guillemots and many other sea-birds have 

 their summer quarters and bring up their family ; one has 

 seen the water-snails browsing nonchalantly on the minute 

 vegetation on the stones of the Niagara River within a few 

 yards of the Falls ; but are any of these habitats so remark- 

 able as that of a spider that lives inside one of the Pitcher- 

 plants ? In that notorious lure for insects, with its very 

 slippery internal surface, and noxious dungeon full of 

 rottenness, the spider lives and thrives. Forestalling the 

 plant, it catches some of the insect victims as they slip 

 down the facilis descensus Averni and sucks their juices, 

 letting the dry corpses tumble into the pit. This is certainly 

 one of the strangest of habitats. They say, moreover, that 

 when an insectivorous bird aware of the plant's device 

 arrives on the scene and proceeds to break down the 

 prison-walls, the spider plunges into the foul fluid in the 

 foot of the pitcher, is able to survive suffocation for a 

 time, and eventually escapes as the tearing-up is accom- 

 plished. 



Larvae of Flies. There is no parallel in the rest of the 

 animal kingdom to the variety of habit and habitat that 

 is illustrated by the larvae of Dipterous insects. Mr. J. C. 

 Hamon found larval Stratiomyidae in a hot spring in 

 Wyoming, where he could not keep his hand immersed, and 

 others occur in brine. Some are found in the making 

 torrent, and others in the rain-water barrel. Some are 

 found in the midst of filth, and others cannot endure the 

 least contamination. Some are parasitic, and others have 

 an extremely active free life. Let us take as an instance 

 in more detail the larva of Simulium reptans, a British 

 representative of the buffalo-gnats. The adult fly bites 

 hard and is irritating to man, but it is not to be compared 



