6 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
makes it possible to examine vital phenomena directly and watch the 
effects of stimuli upon the circulation, etc., in continuo. Many curious 
problems, among them bathymetric distribution and the effects of. 
environment, can be satisfactorily studied in these groups. Itisa 
matter of wonder that greater use is not made of these types in the 
laboratory courses of our universities. Probably the chief obstacle 
has been the lack of suitable means of determining species. This we 
evdeavor to offer in so far as may be necessary for this purpose, but 
purposely abstain from the theoretical questions everywhere pressing 
on the attention. 
This work claims to be a report on the Crustacea of Minnesota, but 
it was found impracticable to sufficiently describe our forms without 
a rapid survey of the whole territory. I am under obligations to Pro- 
fessor C.. Dwight Marsh and to Professor E. A. Birge for loan of litera- 
ture, and to Professor Charles Turner of Atlanta for many notes incor- 
porated in this work. My greatest obligation is to my wife, who has 
collated the bibliography accompanying. This tedious but most useful 
labor has been wholly performed by her. 
For many incidental aids during the progress of the work I am 
indebted to my brother, Professor C. Judson Herrick. 
The reader is requested to remember that this is a revision, follow- 
ing to a large extent the mould set in 1834, and therefore should not 
be held to the standard of a work wholly prepared in the light of our 
present knowledge. 
The third part of this paper, that dealing with the Ostracoda, is 
wholly prepared by Professor C. H. Turner, who has been assiduously 
studying the group for several years, and I feel sure that his contribu- 
tion will be highly appreciated at the present time, especially as no 
attempt to monograph the order in America has yet been made. 
ALBUQUERQUE. NEW MEXI©co, Nov. 1, 1894. 
