1 8 E. V. COWDRY. 



Returning to our Massachusetts brood, there is a gap in our 

 records from 1634 to 1789 but published accounts 9 report the re- 

 appearance of the insects every 17 years from 1789 to 1923. 

 There is every reason to believe that they have, with the utmost 

 regularity, maintained this 1 7-year cycle for upwards of 300 years, 

 with the prospect of continuing indefinitely, or until they are 

 killed out by the removal of underbrush. Undoubtedly the Rick- 

 ettsia-Y\ke microorganisms, to which attention has been called, 

 have selected very remarkable hosts. 



EXPLANATION OF PLATES. 



FIG. i. Intestine of adult " locust," alcoholic fixation, Giemsa's stain, 

 and photograph at 1,000 diameters. 



FIG. 2. Malpighian tubule of adult " locust," same fixation and staining, 

 photograph at 1,000 diameters. 



FIG. 3. Intestine of adult " locust," alcoholic fixation, Gram's stain, and 

 photograph at 1,500 diameters. 



