126 PEEIODICAL CICADA. 



which I have dissected I have found them to vary from three hundred 

 and eighty to four hundred and twenty. 



TIME AND CONDITIONS OF HATCHING. 



Mr. Riley states that in the region of Saint Louis the e^^s of the 

 Seventeen-year Cicada hatch from the 20th of July to the 1st of August. 

 In the latitude of Chicago some of them remain unbatched a month, at 

 least, later. On the 24:th, and again on the 28th, of August, I saw in- 

 dividuals in the act of hatching, though in most instances only empty 

 egg shells could be found. 



As the young locusts obtain their subsistence not on the tree but in 

 the earth, and as many of the twigs stung by the parent insects break 

 off and fall to the ground, carrying the eggs with them, it has been 

 commonly supposed that this constitutes a part of the natural economy 

 of the insect; but this supposition proves to be erroneous. On the 

 contrary, it is found that in the twigs which die, whether they fali 

 to the ground or hang upon the tree, the eggs do not come to maturity, 

 the moisture of the growing twig seeming to be essential to the develop- 

 ment of the eggs. 



Upon examining the eggs in many twigs, in the latter part of Augusts 

 I found, quite uniformly, that in the living twigs the young had hatched 

 and gone, leaving only the white membranous envelopes behind, whilst 

 in the dead twigs the eggs were unhatched, somewhat shrunken, and 

 of a pale-brownish or amber color. Some exceptional eases are seen, 

 where vacant eggs shells are found in dead twigs ; but these cases can 

 be plausibly explained, upon the supposition that though the twigs ul- 

 timately perished they retained their vitality long enough to perfect 

 the enclosed eggs. The sound egg, when near the time of hatching, 

 can always be distinguished from the abortive eggs, not only by their 

 whiter color, but more definitely by the presence of two distinct dark- 

 red spots at one extremity, which are produced by the eyes of the en- 

 closed insect showing through the thin envelope. 



The death of the twig is caused simply by the mechanical violence 

 done to them in ihe act of depositing. Accordingly it is usually only 

 the small terminal part of a twig that perishes, whilst the stouter basal 

 part, which is proportionately less damaged, survives. 



These insects also sometimes, but rarely, perish in the egg from the 

 opposite cause, namely : the too rapid growth of the twig in which they 

 are deposited. This sometimes occurs in thrifty young apple-trees, 

 and in twigs of considerable size, usually as large as a man's finger, 

 where the injury caused by the deposition of the eggs has not been sut- 



