SEVENTEEN-YEAR LOCUST 
SNODGRASS. 409 
imperative with them once their feet have touched the ground. 
See, then, how within a few minutes their instincts shift to opposites. 
On hatching, their first effort is to extricate themselves from the nar- 
row confines of the egg nest. It seems unlikely that enough light 
can penetrate the depths of this chamber to guide them to the exit, 
but once out and divested of their encumbering embryonic clothes 
they are irresistably drawn in the direction of the strongest light, 
even though this takes them upward, just the opposite of their des- 
tined course. But when this instinct has served its purpose and has 
taken the creatures to the port of freest passage to the earth, all their 
love of light is lost or swallowed up in the call to reenter some dark 
hole, narrower even than the one so recently left by such physical 
exertion. 
When the young cicadas have entered the earth we practically have 
to say good-by to them till their return. Yet this recurring event is 
ever full of interest to us, for, as much as the cicadas have been 
studied, it seems that there is still plenty to be learned from them 
each time they make their visit to our part of the world. 
Fig, $.—Youns cicada larva, or nymph, ready to enter the ground (greatly magnified). 
