But if he confine his attention to one class within one country he will soon make up his mind how to rank most of the doubtful forms.

His general tendency will be to make many species, for he will become impressed, just like the pigeon or poultry fancier before alluded to, with the amount of difference in the forms which he is continually studying; and he has little general knowledge of analogical variation in other groups and in other countries by which to correct his first impressions.

As he extends the range of his observations he will meet with more cases of difficulty; for he will encounter a greater number of closely-allied forms.