CHIGGERS — FARRELL 107 



which appeared different by reason of color, conformation, or 

 number of setae were mounted on slides. Specimens of different 

 engorgements were selected. Chiggers were preserved for study- 

 in polyvinyl alcohol with lactic acid on microscope slides. 



A Spencer research microscope was used to study the slides. 

 It was equipped with low power and oil immersion apochromatic 

 objective lenses, high dry and oil immersion dark contrast phase 

 contrast objective lenses, and a turret condenser. Compensating 

 oculars of 5x and lOx were used. Each lens system had its own 

 sphere of usefulness. The phase contrast objectives were most 

 helpful for surface detail and body setae in fresh preparations, 

 but in older and overcleared slides were useful for all structures. 

 Drawings and measurements were made with the aid of a reticule 

 carried in one lOx ocular. To be used for measuring, the reticule 

 was calibrated with a stage micrometer. The edge of one square 

 equaled 61.5 microns with the low power apochromatic objective, 

 14.5 microns with high dry phase, 6.8 microns with the oil im- 

 mersion apochromatic, and 6.3 microns with the phase oil im- 

 mersion. Drawings were made on blue-line graph paper ruled to 

 one-fifth of an inch. Photomicrographs were made with a Spencer 

 photomicrographic camera on the microscope. The oil immersion 

 phase contrast lens and a 5x compensating ocular were used for 

 all photomicrographs. 



All chigger identifications were made at Duke University. Dr. 

 G. W. Wharton identified two new species of Trombicula, the 

 Trombicula near akamushi, and the new genus. Other chigger 

 identifications were made by the author. 



Chiggers of the genus Euschongastm were first sorted out 

 strictly on morphology. A key was developed by which species 

 known in the literature could be identified. Names from the 

 literature were applied temporarily to forms when descriptions 

 seemed to agree with observed morphology. The key was altered 

 and enlarged as the study proceeded. A catalog was kept of all 

 specimens and notes were made of variations and anomalies. 

 After the material had been sorted, each series of specimens was 

 reexamined. If the series was small, all specimens were studied. 

 If the series was large, it was studied by sampling. The sample 

 was taken by picking slides from the slide box at regular inter- 

 vals. In some cases additional samples were needed from certain 

 geographic areas. They were taken at random from the slide box. 

 More detailed notes, including setal counts and measurements of 

 morphological features were made. Within the limits of the 



