12 
to find for this work the trained and intelligent naturalist, 
habituated to the methods of the close observer, whose eye 
nothing escapes, but whose mind rapidly and skilfully sifts the 
miscellaneous offerings of his senses, holding the significant and 
suggestive and letting slip the trivial and the unessential. 
There seem to be among our younger college men ten practical 
embryologists to one good observer. It is, in fact, the biological 
station, wisely and liberally managed, which is to restore to us 
wliat was best in the naturalist of the old school united to what 
is best in the laboratory student of the new. 
On the other hand, the variety of uses which must now be 
made of preserved material in the course of our Station studies 
necessitates the frequent employment of the nicest methods of 
the histological laboratory, and a complete acquaintance, at 
least, with laboratory methods in general. 
Definite and precise comparisons of different aquatic local¬ 
ities with respect to their biology have first been made possible 
in some considerable measure by the comparatively recent intro¬ 
duction of more or less exact quantitative methods for the col¬ 
lection and determination of the biological contents of the water. 
These, commonly known as plankton methods, enable us also to 
study the biological history of any locality to which they are 
fully applicable, by making it possible to bring into close com¬ 
parison the organic contents of the water from day to day, from 
season to season, and from year to year. Unfortunately, these 
methods are not as yet capable of application to all aquatic 
forms in all situations, but have been used successfully only for 
the smaller plant and animal forms of the clear open water. 
By using always identical apparatus in a perfectly uniform 
manner for the accumulation of microscopic and semi-micro- 
scopic objects in such waters and preserving the product by 
identical methods, it is possible to make and keep collections 
which may serve as a means to a precise comparison of the 
mass of organic life in the waters studied, or of the number of 
individuals representing any selected species. 
In our own Station work these plankton operations have 
been carried forward from the beginning at all the substations 
where open water could be found in condition to permit the 
hauling of our plankton net, or, later, the use of the plankton 
pump. A large number of quantitative determinations of col- 
