140 
the recognition of relative morphological values 
he would have prepared a work of signal util- 
ity. The student who uses the ‘ Grundriss’ as 
his guide may acquire a fair knowledge of the 
empirical facts of embryology, but he will still 
have to learn the morphological interpretation 
of these facts and their relative importance. 
Meanwhile he will have profited by better, 
more available and more matter-of-fact descrip- 
tions of the anatomy of embryos than can be 
found in perhaps any other of the smaller text- 
books of embryology. 
C. 8. Minor. 
Das Siisswasserplankton, Methode und Resultate 
der quantitativen Untersuchung. Von DR. 
Cari APSTEIN, Kiel, Zool. Institut. Mit 118 
Abbildungen. Kiel und Leipzig, Verlag 
von. Lipsius & Tischer. 1896. 200 pp., 5 
Tabellen. 
To Dr. Apstein, of the school of planktologists 
at Kiel, is to be given the credit of applying the 
methods employed by Professor Hensen in his 
investigations in the Baltic and North seas, and 
on the ‘ National’ Expedition of 1889, to the 
quantitative investigation of the plankton of 
fresh water. His field of operations has been 
the lake region of Holstein. The book con- 
tains a full report of the results of the quantita- 
tive, and to some extent the qualitative, ex- 
amination of more than 300 collections made in 
15 different lakes during 1890-1895. A de- 
scription is given of the apparatus, methods of 
collection, of determination of volume, and of 
enumeration of the constituent organisms or 
planktonts, if we adopt the term recently in- 
troduced by Schroter. Thereis, unfortunately, 
no adequate discussion of the margin of error 
which the methods involve. An annotated 
list of the important limnetic organisms is given 
with data on the seasonal distribution, abun- 
dance with dates of maximum and minimum 
occurrence and reproductive activity, with other 
facts of cecological import. Many of the forms 
are illustrated by reproductions from original 
microphotographs by the author. The micro- 
scope in the hands of the skillful operator re- 
veals vastly more than the ordinary micro- 
photograph records. For the purposes of scien- 
tific illustration of organisms of the plankton, 
SCIENCE. 
[N.S. Vou. VI. No. 134. 
and especially in such a book as this, it seems 
undesirable to substitute a method which rests 
upon the relative opacity of tissues simply, for 
one based upon the clear interpretation of the 
trained observer. One has only to contrast 
Dr. Apstein’s best results in this line with the 
figures he reproduces from Hudson and Gosse, 
and Lauterborn, to appreciate the superiority of 
a carefully made drawing in conveying to the 
inquirer details of structure, and even such 
features as contour, proportion and natural 
position of parts. The book is not a manual of 
the limnetic fauna and flora, and the noyice 
and casual student must still depend upon 
monographs and the widely scattered literature 
of the subject for aid in the determination of 
the planktonts. It is, however, an epitome of 
the subject, indispensable to every planktolo- 
gist and a valuable aid to every student of fresh- 
water fauna. 
Our author distinguishes active, passive 
and tycho-limnetic forms among the planktonts. 
With the latter he places Difflugia, whose pres- 
ence in the open water is attributed to gas 
vacuoles, which cause it to rise from the bottom, 
its true habitat. Diffiugia is a very abundant 
and important member of the plankton of our 
own great lakes, where it occurs in association 
with Codonella, Dinobryen and other typically 
limnetic forms. It also occurs in the Illinois 
river and its adjacent waters throughout a con- 
siderable part of the year, but in the open water 
and not upon the bottom. The conditions of 
the occurrence are such as to place it among 
the active members of the plankton rather than 
among those which owe their presence to the 
accidents of wind and current. 
Following up the line of his earlier work, 
Apstein brings forward a long series of obseryva- 
tions in proof of the equal horizontal distribu- 
tion of the plankton in a body of water. In 
80 catches the greatest departure from the 
mean was 22.8%, and the average departure 
but 5.52%. These hauls are distributed in short 
series of 2-5 parallel catches in various lakes, but 
the distance separating the successive collections 
isnot given, and in no case has a lake been sub- 
jected to a larger number of examinations made 
upon the same day at frequent and regular dis- 
tances throughout its whole extent. It seems 
