During the summer of 1936 and 1937, in connection with a parasitological study, 502 yellow perch (Perca flavescens Mitchill) were examined from Douglas Lake, Cheboygan County, Michigan. As perch under 10 cm. in total length were found not to contain the nematode being studied, no effort was made to obtain specimens under that size limit. In 1936, it was noticed that there was an extremely unbalanced sex ratio with a very large predominance of females. Therefore, during the past summer, records were kept in hope of determining the sex ratio of the perch in the particular part of the lake being studied.