148 
SCIENCE. 
justified in seeking for our earliest representatives of the 
orders such Echinoderms as resemble the early stages of 
our embryos, and in following, for them as for the Echini, 
the modifications of typical structures. These we shall 
have every reason to expect to find repeated in the fossils 
of later periods, and, going back a step further, we may 
perhaps get an indefinite glimpse of that first Echinodermal 
stage which should combine the structural features common 
to all the earliest stages of our Echinoderm embryos. 
And yet, among the fossil Echinoderms of the oldest 
periods, we have not as yet discovered this earliest type 
from which we would derive either the Star-fishes, Ophiu- 
rans, Sea-urchins, or Holothurians. With the exception of 
the latter, which we can leave out of thequestion at present, 
we find all the orders of Echinoderms appearing at the same 
time. But while this is the case, one of the groups attained in 
these earliest days a prominence which it gradually loses with 
the corresponding development of the Star-fishes, Ophiurans, 
and Sea-urchins, it has steadily declined in importance; it is a 
type of Crinoids, the Cystideans which culminated during 
Paleozoic times, and completely disappeared long before 
the present day. If we compare the early types of Cysti- 
deans to the typical embryonic Echinodermal type of the 
present day, we find they have a general resemblance, and 
that the Cystideans and Blastoids represent among the fossil 
Echinoderms the nearest approach we have yet discovered 
to this imaginary prototype of Echinoderms. 
This may not seem a very satisfactory result to have at- 
tained. It certainly has been shown to be an impossibility 
to trace in the paleontological succession of the Echini any- 
thing like a sequence of genera. No direct filiation can be 
shown to exist, and yet the very existence of persistent 
types, not only among Echinoderms, but in every group of 
marine animals, genera which have continued to exist with- 
out interruption from the earliest epochs at which they occur 
to the present day, would prove conclusively that at any 
rate some groups among the marine animals of the present 
day are the direct descendants of those of the earliest geo- 
logical periods. When we come to types which have not 
continued as long, but yet which have extended through 
two or three great periods, we must likewise accord to their 
latest representatives a direct descent from the older. The 
very fact that the ocean basins date back to the earliest geo- 
logical periods, and have afforded to the marine animals the 
conditions most favorable to an unbroken continuity under 
slightly varying circumstances, probably accounts for the 
great range in time during which many genera of Echini 
have existed. If we examine the interlacing in the succes- 
sion of the genera characteristic of later geological epochs, 
we find it an impossibility to deny their continuity from the 
time of the Lias to the present day. The Cidaris of the Lias 
and the Rhabdocidaris of the Jura are the ancestors of the 
Cidaris of to-day. The Saleniae of the lower Chalk are those 
of the Saleniae of to-day. Acrosalenia extends from the 
Lias to the lower Cretaceous, with a number of recent 
genera, which begin at the Eocene. The Pygasterof to-day 
dates back to the Lias ; Echinocyamus and Fibularia com- 
mence with the Chalk. Pyrina extends from the lower Jura 
through the Eocene. The Echinobrissus of to- day dates back 
to the Jura. Ilolaster lived from the lower Chalk to the 
Miocene, and the Ilemiaster of to-day cannot be distin- 
guished from the Hemiaster of the lower Cretaceous. 
Such descent we can trace, and trace as confidently as we 
trace a part of the population of North America of to-day as 
the descendants of some portion of the population of the 
beginning of this century. But we can go no further with 
confidence, and bold indeed would he be who would at- 
tempt even in a single State to trace the genealogy of the 
inhabitants from those of ten years before. We had better 
acknowledge our inability to go beyond a certain point ; any- 
thing beyond the general parallelism I have attempted to 
trace, which in no way invalidates the other proposition, we 
must recognize as hopeless. 
But in spite of the limits which have been assigned to 
this general parallelism, it still remains an all-essential factor 
in elucidating the history of paleontological development, 
and its importance has but recently been fully appreciated. 
For, while the fossil remains may give us a strong presump- 
tive evidence of the gradual passage of one type to another, 
we can only imagine this modification to take place by a pro- 
cess similar to that which brings about the modifications due 
to different stages of growth, — the former taking place in what 
may practically be considered as infinite time when compared 
to the short life history which has given us as it were a 
rdsumS of the paleontological development. We may well 
pause to reflect that in the two modes of development we find 
the same periods of rapid modifications occurring at certain 
stages of growth or of historic development, repeating in a 
different direction the same phases. Does it then pass the 
limits of analogy to assume that the changes we see taking 
place under our own eyes in a comparatively short space of 
time, — changes which extend from stages representing per- 
haps the original type of the group to their most complicated 
structures, — may, perhaps, in the larger field of paleontolog- 
ical development, not have required the infinite time we are 
in the habit of asking for them ? 
Paleontologists have not been slow in following out the 
suggestive track, and those who have been anatomists and 
embryologists besides have not only entered into most in- 
teresting speculations regarding the origin of certain 
groups, but they have carried on the process still further, 
and have given us genealogical trees where we may, in the 
twigs and branches and main limbs and trunk, trace the 
complete filiation of a group as we know it to-day, and as 
it must theoretically have existed at various times to its 
very beginning. While we cannot but admire the boldness 
and ingenuity of these speculations upon genetic connec- 
tion so recklessly launched during the last fifteen years, we 
find that with but few exceptions there is little to recom- 
mend in reconstructions which shoot so wide of the facts 
as far as they are known, and seem so readily to ignore them. 
The moment we leave out ol sight the actual succession of 
the fossils and the ascertainable facts of post-embryonic de- 
velopment, to reconstruct our genealogy, we are building 
in the air. Ordinarily, the twigs of any genealogical tree 
have only a semblance of truth ; they lead us to branchlets 
having but a slight trace of probability, to branches where 
the imagination plays an important part, to main limbs 
where it is finally allowed full play, in order to solve with 
the trunk, to the satisfaction of the writer at least, the riddle 
of the origin of the group. It seems hardly credible that a 
school which boasts for its very creed a belief in nothing 
which is not warranted by common sense should descend 
to such trifling. 
The time for genealogical trees is passed ; its futility can, 
perhaps, best be shown by a simple calculation, which will 
point out at a glance what these scientific arboriculturists 
are attempting. Let us take, for instance, the ten most 
characteristic features of Echini. The number of possible 
combinations which can be produced from them is so great 
that it would take no less than twenty years, at the rate of 
one new combination a minute for ten hours a day, to pass 
them in review. Remembering now that each one of these 
points of structure is itself undergoing constant modifica- 
tions, we may get some idea of the nature of the problem 
we are attempting to solve, when seeking to trace the gene- 
alogy as understood by the makers of genealogical trees. 
On the other hand, in spite of the millions of possible com- 
binations which these ten characters may assume when 
affecting not simply a single combination, but all the com- 
binations which might arise from their extending over 
several hundred species, we yet find that the combinations 
which actually exist — those which leave their traces as fos- 
sils — fall immensely short of the possible number. We 
have, as I have stated, not more than twenty-three hundred 
species actually representing for the Echini the results of 
these endless combinations. Is it astonishing, therefore, 
that we should fail to discover the sequence of the genera, 
even if the genera, as is so often the case, represent, as it 
were, fixed embryonic stages of some Sea-urchin of the 
present day ? In fact, does not the very history of the fossils 
themselves show that we cannot expect this ? Each fossil 
species, during its development, must have passed through 
stages analagous to those gone through by the Echini of 
the present day. Each one of these stages at every moment 
represents one ol the possible combinations, and those 
which are actually preserved correspond only to the parti- 
cular period and the special combination which any Sea- 
urchin has reached. These stages are the true missing 
links, which we can no more expect to find preserved than 
we can expect to find a record of the actual embryonic de- 
velopment of the species of the present day without direct 
