988 
regressive, progressive, parallel, aberrant) and 
the meaning of each term is clearly explained. 
That variation is nearly always significant 
and that its significance may be determined 
are two cardinal principles which the reader 
of this book can scarcely doubt. 
The terminology adopted by Jackson is as 
free from technicalities as possible and there 
are scarcely any new terms introduced. Those 
which are proposed, as for example “ mid- 
zone,” are simple, readily understood and meet 
a real need. In the case of such terms as 
have been used in different senses by previous 
authors, as “peristome,” Jackson has adopted 
that usage which has appealed to him as 
simplest and least open to misunderstanding, 
and consequently even those who prefer a 
different sense can not mistake his meaning. 
The extensive investigations which Jackson 
has made into the morphology of Recent 
echini have led him to some interesting dis- 
coveries of structures hitherto overlooked. A 
notable illustration of this is the presence or 
absence of pits in the upper end of the half- 
pyramids which compose the lantern. These 
pits have apparently been overlooked hitherto, 
though they seem to be of real systematic im- 
portance and even of ordinal value. 
In his choice of generic and specific names 
Jackson has followed the International Code, 
but not at the expense of his judgment or 
common sense. As an illustration of his men- 
tal attitude, his sensible treatment of Archwo- 
cidaris vs. Echinocrinus is illuminative. No- 
body questions that Echinocrinus has priority, 
but Jackson well says: “ This name, however, 
is misleading, was based by Professor Agassiz 
on a misconception of affinities and has been 
abandoned for some sixty years in favor of the 
entirely appropriate Archeocidaris of McCoy. 
... To revive the old name Echinocrinus .. . 
will make confusion at present and in future, 
and no gain to any one.” Another taxonomic 
snarl which Jackson has courageously un- 
tangled is that involving the name Diadema. 
For years it has been known that this name 
belongs to a cirriped. although it has also been 
in use for a genus of butterflies and for one 
of the best-known genera of tropical sea- 
SCIENCE 
[N.S. Vou. XXXV. No. 913 
urchins. Students of the echini have per- 
sisted in its use and a family and an ordinal 
name based upon it are both universally 
adopted. Jackson’s statement of the case (p. 
27) is clear and convincing and his proposed 
substitutes Centrechinus, Centrechinide and 
Centrechinoida are appropriate and euphoni- 
ous. Now that the Gordian knot is cut, it is 
to be hoped that zoologists will no longer use 
Diadema for either sea-urchin or butterfly. 
Following his introductory pages, Jackson 
divides his book into three parts. The first of 
these is entitled “ Comparative Morphology of 
Echini.” It includes 168 pages, crowded with 
observations and interpretations of the typical 
structure of the test and lantern, and varia- 
tions therefrom. One notes the absence of 
any discussion of the pedicellariz and of the 
non-caleareous organs, but as these parts seem 
to have little phylogenetic significance the 
omission is perhaps not important. We may, 
however, hope that some zoologist will be 
moved to institute ere long a similar thorough . 
comparative study of these less significant sys- 
tems. So far as the pedicellarie are con- 
cerned, Mortensen already has accumulated a 
mass of important material. Jackson’s open- 
ing paragraph is a fine defense of the claim 
that paleozoology is only one aspect of zool- 
ogy. Then follow sections on the form of the 
test, orientation, the pentamerous system and 
variation therefrom, the structure of the skele- 
ton, growth, ambulacrum of the corona, inter- 
ambulacrum, basicoronal plates, imbrication, 
spines, peristome, ocular and genital plates, 
periproct, Aristotle’s lantern and perignathic 
girdle. It is impossible in a review like this 
to give any adequate conception of the wealth 
of these sections; only the most striking fea- 
tures may be noted. The repeated references 
to Lovén and his work show in what high 
esteem he is held, while the constant emphasis 
on the significance of both normal structures 
and variations is very noticeable. Variants 
from pentamerous symmetry are shown to be 
exceedingly rare; only 25 were recorded prior 
to Jackson’s work, but he has studied 71, of © 
which 60 were found in the fifty thousand 
Recent echini personally examined by him. 
