Chap. II. 
DOUBTFUL SPECIES. 
49 
be doubted would be ranked as distinct species by many 
entomologists. Even Ireland has a few animals^ now 
generally regarded as varieties, but which have been 
ranked as species by some zoologists. Several most 
experienced ornithologists consider our British red 
grouse as only a strongly-marked race of a Norwegian 
species, whereas the greater number rank it as an 
undoubted species peculiar to Great Britain. A wide 
distance between the homes of two doubtful forms leads 
many naturalists to rank both as distinct species; but 
what distance, it has been well asked, will suffice ? if 
that between America and Europe is ample, will that 
between the Continent and the Azores, or Madeira, or 
the Canaries, or Ireland, be sufficient? It must be 
admitted that many forms, considered by highly-compe- 
tent judges as varieties, have so perfectly the character 
of species that they are ranked by other highly-compe- 
tent judges as good and true species. But to discuss 
whether they are rightly called species or varieties, 
before any definition of these terms has been generally 
accepted, is vainly to beat the air. 
Many of the cases of strongly-marked varieties or 
doubtful species well deserve consideration; for several 
interesting lines of argument, from geographical dis¬ 
tribution, analogical variation, hybridism, &c., have 
been brought to bear on the attempt to determine their 
rank. I will here give only a single instance,^—^the 
well-known one of the primrose and cowslip, or Primula 
vulgaris and veris. These plants differ considerably in 
appearance; they have a different flavour, and emit a 
different odour; they flower at slightly different periods; 
they grow in somewhat different stations ; they ascend 
mountains to different heights; they have different 
geographical ranges ; and lastly, according to very 
numerous experiments made during several years by 
D 
