SYSTEMATIC PART. 167 
the same reason we cannot point out the exact consanguinity of groups 
which are apparently related by one or more characters. For we find that 
when a type starts on a career of development on a specialized line and 
runs its course, other characters for the time being subordinated to it follow 
in more or less parallel successions. So that it may come to pass that at 
a certain time we find two types apparently belonging to different lines of 
development, which have reached a concurrent condition in some other 
important character, and we cannot say through which of them the thread 
of consanguinity has been carried. For instance, in the non-typical Camerata 
we have the Platycrinide without an anal plate accompanied and succeeded 
by the Hexacrinide, in which that plate is present. In the typical section 
the Melocrinidz are followed by the Batocrinide and Actinocrinidx in 
similar succession. But (according to our paleontological record) the sym- 
metric Platycrinidx appear at a somewhat later period than the symmetric 
Melocrinide ; — and as we do not find in the non-typical section any sym- 
metric predecessors of the Platycrinidee, we would be inclined on this 
ground to infer that they were derived from the Melocrinide. But here 
we are met by a greater difficulty, for this involves the illogical supposition 
that the Platycrinidse — a family of the least development of the Camerate 
type 
line. 
are derived from one much more highly organized in that particular 
The trouble is that all our generalizations are necessarily based upon the 
Crinoids as they are represented in our museums, and not upon the Crinoids 
as they actually existed in geological time, which is a very different thing. 
It is like trying to reconstruct a book from detached fragments of the 
chapters, some of them written in hieroglyphics for whose decipherment the 
key has not yet been found. We are accustomed to speak of the imper- 
fection of the geological record, but it is doubtful if in our practical studies 
we always bear in mind what this really means. To say nothing of the 
periods antedating the Silurian, in which substantially all vestiges of life are 
obliterated by metamorphism; of the accumulations of fossiliferous strata 
which have been destroyed by erosion during periods of elevation of the sea 
bottom; of the strata which over three fifths of the earth are submerged 
beneath the ocean; of the great regions unexplored, or covered with ice, 
snow, or sand; of the equally extensive areas in which the fossiliferous 
rocks of one formation are buried under those of succeeding ones ; — leaving 
all this out of consideration, how much do we actually know of the life 
