No. 388.] FOUR CATEGORIES OF SPECIES. 289 
The species of the paleontologist is, then, with reference to 
the other members of its line, an arbitrary division of a contin- 
uous series of gradually changing forms. The fact of estab- 
lished sequence will go far to prevent confusion, and the 
purposes of classification are served by such a knowledge of — 
forms and characters as will make possible the reference of a 
given individual to its proper place inthe series. Illogical pro- 
cedure may be charged against any attempt at applying these 
concepts or methods outside of the lines of established, or at 
least suspected, phylogeny. 
The termini of such of the paleontological series as have not 
become extinct are the subject-matter of the biology of to-day, 
in contradistinction to that of the past or the future. Return- 
ing to the former analogy, it may be insisted that as the accre- 
tions of the life of previous ages have been built up on distinct 
lines, so is existing life manifested in assemblages of simi- 
lar individuals, which are obviously distinct collectively. The 
forms which would be required to connect them do not exist, 
and we shall make little true progress in the knowledge of 
organic nature until we abandon the attempt at arranging living 
organisms in continuous series. With rare exceptions their 
relationship must be traced through the more or less remote 
past. In one sense all life may be thus connected, and abso- 
lute lines between groups of specific or higher rank are forever 
impossible; but in another and equally important sense groups 
of living organisms may be looked upon as separate and inde- 
pendent, though collective, entities. The study of geography 
has not been abandoned because of the discovery that all land 
is connected by the ocean bottom, nor is the topography of a 
series of islands neglected because soundings prove that they 
are peaks of a submerged mountain range. No naturalist de- 
nies the existence of clearly defined and easily recognizable 
specific groups, but the difficulty experienced in attempting to 
resolve the more nebulous parts of nature has sometimes blurred 
the eyesight of the systematist. In some generic archipelagoes 
the specific islands stand out prominent and distinct, like the 
members of the Canary and Hawaiian groups; while in others 
they are painfully similar and are separated only by narrow, 
