10^ PROCEEDINGS OF THE NATIONAL MUSEUM vOL. 106 



in the center of the silk. Two or three chiggers were removed by 

 dissecting needle from the surface of the water in the collecting 

 vessel and floated on the drop of water. The palmar surface of 

 the forearm was placed on top of the assembly, which was secured 

 in place by the adhesive tape. From 41/2 to 7 hours later the 

 applications were removed, and the areas were examined with a 

 dissecting microscope. 



Chiggers were used in experiments to determine their rates of 

 locomotion during falling and rising temperatures. Two species 

 of chiggers, T. alfreddugesi with a warm weather distribution and 

 E. peromysci with a predominantly cold weather distribution, 

 were compared in the tests. Clean glass tubes, 76 mm. or 40 mm. 

 by 7 mm., were used to confine the chiggers. One or two specimens 

 were placed in each tube. The two species were placed in separate 

 tubes. The tubes were stoppered at each end with clean rubber 

 stoppers. An apparatus to produce a slowly falling temperature 

 was made by mixing salt and crushed ice in a trough. A shelf 

 of hardware cloth was suspended in the freezing mixture. A 

 small finger bowl was filled with brine solution and placed on 

 the shelf. The tubes containing the chiggers and the bulb of a 

 thermometer were submerged in the finger bowl. To obtain rising 

 temperatures, the finger bowl was removed from the freezing 

 mixture to room temperature. To produce temperatures above 

 that of the room, hot water from the laboratory supply line was 

 led into the trough by a length of hose; and the finger bowl was 

 returned to the hardware cloth shelf. Light from a dissecting 

 microscope lamp was directed on the chiggers, and a dissecting 

 microscope with an ocular micrometer was used to observe them. 

 The chiggers were timed with a stop watch as they moved 

 through the tubes. 



In a second test a dead Peromyscus leucopus (Rafinesque), 

 infested with chiggers, was placed in a freezing chamber at 

 — 4.5^ C. on Mar. 20, 1949. It remained in the chamber at that 

 temperature until it was removed on Apr. 27, 1949, and placed 

 in a funnel over water. 



A selective process was used to determine chiggers for preser- 

 vation on slides. Every effort was made to obtain specimens of 

 all species represented in a collection. Whenever there were many 

 specimens from which a sample was to be mounted on slides, a 

 search was made for different forms. The dissecting microscope 

 was frequently used to examine living material. It was always 

 used with specimens already preserved in alcohol. Any specimens 



