366 KEV. J. T. GULICK ON" 



months. The imago appears late in May, and for a little more 

 than a month the males make the woods ring with their shrill 

 stridulatious. The eggs, which are deposited in the green twigs 

 of trees, mature during the latter part of July ; and each newly- 

 hatched larva dropping to the ground, takes up a solitary subter- 

 ranean life, which it follows till its period of 17 years is nearly 

 comj)lete. It then appears above the ground, passes into its 

 winged stage, and enters on a few weeks of social life which 

 closes its career. This species is widely distributed in that part 

 of the United States that lies between the Atlantic shore and the 

 Eocky Mountains. It does not, however, occur in Minnesota, 

 Northern Michigan, or Northern New England. It is, however, 

 represented by two races in every respect the same, except that 

 one has a life-history of thirteen and the other of seventeen years. 

 The 13-year race prevails in the Gulf States, while in New Eng- 

 land and the Middle States the 17-year race is alone found. In 

 Illinois, Missouri, Kansas, and in several of the Southern States 

 the two races occur in the same localities : but it is evident that 

 even in such localities it is only once in 221 years that there will 

 be any opjDortunity for crossing between them, and we are 

 informed by those who have made a special study of the svibject 

 that they do not cross when these opportunities occur. 



These two races are therefore protected by partial Local Se- 

 gregation ; by Cyclical Segregation rendering it impossible that 

 a brood of each occupying the same locality should have oppor- 

 tunity for crossing more than once in 17 generations of the shorter- 

 lived race, or once in 13 generations of the longer-lived race ; and 

 by Sexual Segregation that shows itself in diversity of instincts 

 preventing them from pairing when other conditions favour. 



Whether devices have been tried to induce cross-unions, and 

 whether such unions are unfruitful, I have never heard ; but the 

 simple fact that 15-year forms do not appear in localities where 

 the two races are found, indicates that in nature they do not 

 cross. Several such localities have been reported, but in none of 

 them has an intermediate form been found. It seems, therefore, 

 that we may safely draw the conclusion that we have here a case of 

 complete Sexual Segregation between forms which to the human 

 eye are undistinguishable, and which call their mates with stri- 

 dulatious which to the human ear are the same. Now I claim that 

 in such races as these we have the beginning of divergent species — 

 a beginning that lies in the segregative influences of constitutional 



