Mr. Walsh ranks the forms which it may be supposed would freely intercross, as varieties; and those which appear to have lost this power, as species. 查尔斯·达尔文.物种起源.
Walsh, a distinguished entomologist of the United States, has described what he calls Phytophagic varieties and Phytophagic species. 查尔斯·达尔文.物种起源.