Chap. II. 
DOUBTFUL SPECIES. 
51 
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. But if his observations be widely extended, he 
will in the end generally be enabled to make up his own 
mind which to call varieties and which species; but he 
will succeed in this at the expense of admitting much 
variation,—and the truth of this admission will often be 
disputed by other naturalists. When, moreover, he 
comes to study allied forms brought from countries not 
now continuous, in which case he can hardly hope to 
find the intermediate links between his doubtful forms, 
he will have to trust almost entirely to analogy, and his 
difficulties rise to a climaxo 
Certainly no clear line of demarcation has as yet 
been drawn between species and sub-species—that is, 
the forms which in the opinion of some naturalists come 
very near to, but do not quite arrive at the rank of 
species ; or, again, between sub-species and well-marked 
varieties, or between lesser varieties and individual dif¬ 
ferences. These differences blend into each other in an 
insensible series; and a series impresses the mind with 
the idea of an actual passage. 
Hence I look at individual differences, though of 
small interest to the systematise as of high importance 
for us, as being the first step towards such slight varieties 
as are barely thought worth recording in works on natural 
history. And I look at varieties which are in any degree 
more distinct and permanent, as steps leading to more 
D 2 
