54 
SCIENCE. 
SCIENCE: 
A Weekly Record of Scientific 
Procress. 
JOHN MICHELS, Editor. 
Published at 
229 BROADWAY, NEW YORK 
P. O. Box 3838. 
SATURDAY, JULY 31, 1880. 
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Broadway. 
PROFESSOR LEIDY’S “ FRESH WATER RIIIZO- 
PODS OF NORTH AMERICA.” 
Dr. Leidy is acknowledged to be the highest 
authority on the subject treated in his great work, 
“ Fresh Water Rhizopods of North America ; ” a 
criticism of the book becomes, therefore, a work of 
supererogation, and we reserve to ourselves the 
more pleasing task of pointing out its many beau- 
ties and particularly its importance as one of the 
most valuable contributions to the literature of 
microscopic forms of life. 
Published by the Department of the Interior of 
the United States Government, and forming volume 
twelve of the “ Report of the United States Geo- 
logical Survey of the Territories” in charge of 
Professor F. V. Hayden, it is produced in a sump- 
tuous form which no private publisher would have 
dared to imitate. 
Dr. Leidy’s Report covers about three hundred 
folio pages, illustrated by forty-eight full sized 
plates, printed in colors in the highest style of 
lithography. 
It may be a superfluous question to most of our 
readers, but as Dr. Leidy himself inquires in the first 
page of his work, “ What are Rhizods?” In re- 
ply he says, “ Rhizopoda are the simplest and 
lowest forms of animal life, constituting the first 
class of the Protozoa. They derive their name 
from the Greek word rhiza , a root, and pous , a 
foot. They are mostly microscopic beings, al- 
though sometimes sufficiently large to appear as 
conspicuous objects.” We may add that the 
essential characters are the gelatinous structureless 
bodies, and the locomotive organs consisting of 
variable retractile root like processes (pseudo-poda 
or false feet). 
Their minuteness is compensated for by their 
multitude and wide-world distribution ; essentially 
aquatic they occur wherever there is moisture ; the 
search for them may be commenced in the crevices 
of the stones at your door step, and may be con- 
tinued in every marsh, pool, ditch, pond, lake, sea 
and ocean, and from the greatest depths of the latter 
to the snow lines of mountains. 
The particular Rhizopods which form the subject 
of the book now under consideration, are those 
found in fresh water only, and Dr. Leidy expressly 
states that his attention, during the four years en- 
gaged, was directed more to the discovery and de- 
termination of the various forms occurring in the 
United States, than to the elaboration of details of 
structure, habits, modes of development, and other 
matters pertaining to their history. 
Although it is professedly an illustrated catalogue 
of the fresh water Rhizopoda of North America, 
we find most interesting and valuable contributions 
to their life history which makes us regret that time 
and opportunity did not permit Dr. Leidy to extend 
his observations in this direction, for we know how 
exhaustive such a treatise would have been from his 
hands. 
Instead of writing a discursive essay upon Dr. 
Leidy’s book, already done by many brillant 
writers, which, with a work so purely technical, 
seems the least profitable method of treating the sub- 
ject, we propose to take our readers through the book, 
acting the part of a friendly guide, trusting by the 
aid of twenty-two illustrations we have reproduced 
for this purpose, not only to do justice to the work 
in question, but to convey to those who have not 
