cclxvii 



•clock, the moving power being a weight, from which a string passes around 

 the axle of the drum. The drum rotates once in 12 hours. At the end of 

 this time the clock strikes for 12 hours, and, as the striking is finished, the 

 descending clock-weight strikes a spring, releasing a weight which deflects 

 the revolving drum longitudinally half an inch. 'The drum is then in posi- 

 tion to record the succeeding 12 hours. This instrument can be extempo- 

 rized in any properly equipped laboratory. 



LOCUST EXPERIENCE. 



Mr. Rile) made some extended remarks on the locust problem, 

 ■of which the following is a synopsis: 



During his recent trip to British America, he had been able to clear ly 

 define the Northern limit of the insect's permanent breeding grounds as not 

 extending beyond the third prairie steppe or plateau. It often extended in 

 its migrations across the second and first prairie steppes, but very rarely 

 reached beyond the North Saskatchewan. The experience of the year had 

 been most valuable, and matters relating to the Rocky Mountain locust 

 had turned out precisely as he had, from time to time, anticipated. In his 

 studies of this insect he had previously been able to deduce three general 

 rules which might be stated as laws governing the insect in the Lower 

 Missouri and Mississippi valleys. These were, first, the Northwest origin 

 of the more wide-spread and disastrous swarms; second, the return migra- 

 tion toward the Northwest of the insects that hatch in the country South 

 of the 44th parallel and East of the 100th meridian ; third, the Eastern 

 limit of the insects' spread, at a line broadly indicated by the 94th meri- 

 dian. All these rules had been strengthened and borne out by the present 

 year's experience. Mr. Riley was now able to add a fourth rule, viz., that 

 this locust seldom, if ever, lays eggs thickly for two consecutive years in 

 the same locality. He remarked that there was a deal of consolation in 

 this rule for our Western farmers, since it was a guarantee that a year 

 of thick hatching and great devastation will be followed by a year of 

 immunity. 



MITE TRANSFORMATIONS. 



Mr. Riley gave an account of his observations and experi- 

 anents on Astoma gryllaria LeBaron. 



He has, during the summer, proved by experiment that, as he first sug- 

 gested over three years since would be the case, this little six-legged mite, 

 which preys parasitically on the winged locusts, is the larval form of 

 Trombidium sericenm Say, a larger, eight-legged mite that preys upon the 

 eggs of the locust. Hatching from minute eggs laid in loose masses in the 

 ground, Astoma the form crawls on to the locust, fastening and swelling 

 as a tick does on a dog. The Astoma at last drops from the locust to the 

 ground, where it slowly goes through its transformation into the Trombi- 

 dium. As wherever the locusts abound this Trombidium also necessarily 



