JUNE 28, 1912] 
is seriously handicapped when he deals with a 
group, which is poorly represented in nature’s 
great museum, the earth’s crust, and happy is 
he if he can find abundant material in that 
wonderful storehouse. Doubly fortunate is he 
-if his training enables him to get the most 
from such material. One of the greatest ab- 
surdities of our persistent and no doubt neces- 
sary tendency to classify men as well as ob- 
jects is the grouping by themselves as “ pale- 
ontologists ” those who have had this training 
and who specialize in the study of fossil 
organisms. For if a man who uses as his 
material the long-dead and oftentimes badly 
preserved animals of our museums is a. zool- 
ogist, is not the man who studies in the-same 
way similar remains preserved in the strata 
of the earth, just as truly one? Do either the 
length of time since the death of the animal 
or the method by which its remains have been 
preserved matter? Perhaps a line might be 
drawn between those who study fossils simply 
as indicators of geological horizons having in 
view the history of the earth as an object by 
itself, and those who study them as the re- 
mains of living beings whose structure throws 
light on the problems of phylogeny, but the 
latter at least are zoologists (or botanists, as 
the case may be) and when they combine with 
their paleozoology thorough knowledge of the 
structure and development of Recent animals, 
they make the best possible phylogenists. 
When such a worker selects for study a small 
sharply-defined group with a rich geological 
history and abundant Recent material avail- 
able, and devotes years of time and the most 
unflagging industry to his task, the results 
ean not fail to be of prime importance to 
zoologists of all sorts, everywhere. 
Few groups of animals are better adapted 
for such study than the echini. So sharply 
defined is the class that its ancestry is hidden 
in oblivion and not a single connecting link 
with any other class is known. There is no 
animal either Recent or fossil of which it 
can not be affirmed either “this is” or “this 
is not an echinoid.” Moreover, the class is 
relatively small, only about five hundred living 
species being known with perhaps three times 
SCIENCE 
987 
as many fossil. The latter occur in all geo- 
logical periods from the Ordovician to the 
Recent. Much of this material is beautifully 
preserved too, at least so far as essential struc- 
tures go, for the hard test and lantern of a 
sea-urchin are exceptionally satisfactory ob- 
jects for geological preservation. Finally sea- 
urchins have long been favorite objects of 
study, and their anatomy, development and 
life history are as well known as those of any 
marine invertebrates. If, therefore, the in- 
vestigation be undertaken by the right man, 
the possibility of really working out the his- 
tory of the group, were unusually favorable, 
and it is but the simple truth to say that in 
his “Phylogeny of the Echini” Dr. R. T. 
Jackson has shown himself to be that man. 
This monumental work sets forth the actual 
developmental and evolutionary history of the 
echini so fully, so fairly and so convincingly 
that it may be said with little fear of contra- 
diction, there is no other group of animals of 
equal importance the main lines of whose 
phylogeny are more definitely and certainly 
known. Moreover so extraordinary is the 
amount of accumulated fact and so suggestive 
are the interpretations offered that there is 
something of interest in the volume for every 
one attracted by the problems of evolution, be 
he zoologist or botanist. 
The book is dedicated most appropriately 
to Alexander Agassiz and Alpheus Hyatt, the 
former the Nestor of students of echini, the 
latter the originator or promoter of the prin- 
ciples and methods to which Jackson is him- 
self so ardently loyal. Indeed the most 
striking characteristics of the volume are the 
emphasis placed on “stages in development ” 
and the persistence with which the facts are 
marshalled in support of the “recapitulation 
theory.” Those who deny the existence of 
stages and the validity of the recapitulation 
theory will find it exceedingly difficult, if not 
impossible, to meet the arguments and inter- 
pretations with which the writer defends his 
position. Second only to the emphasis on 
stages is the stress laid on variation and its 
significance. In the introductory pages, vari- 
ations are grouped under five heads (arrested, - 
