A CENTURY OF ZOOLOGY IN AMERICA 425 



report on the Batrachia of North America 7 is the stand- 

 ard taxonomic work. 



The most comprehensive systematic work on fishes is 

 the "Descriptive Catalogue of the Fishes of North and 

 Middle America " by Jordan and Evermann. 8 



The invertebrate groups have been in part similarly 

 monographed by the members of the U. S. National 

 Museum staff and others, and further studies are in prog- 

 ress. Other taxonomic monographs published by this 

 museum include the various groups of animals from 

 many different parts of the world. 



A number of the larger State, municipal, and university 

 museums publish bulletins on special groups represented 

 in their collections as well as articles of general zoological 

 interest. 



Expeditions, subsidized by museum and private funds, 

 are from time to time sent to various parts of the world 

 and their results are often published in sumptuous 

 manner. 



The total number of living species of animals is 

 unknown, but considering that about a quarter of a mil- 

 lion new species have been described during the past 

 thirty years, it is probable that several million species are 

 in existence to-day. More than half a million have been 

 described. These are probably but a small fraction of 

 the number that have existed in past geological ages. 



Thus, in spite of all the work that has been done in sys- 

 tematic zoology and as the number of known species con- 

 tinues to increase, there still remain many groups of 

 animals, some of which are by no means rare or minute, 

 in which probably only a small proportion of the species 

 are as yet capable- of identification. 



It is only since the publication of Ward and Whipple 's 

 "Fresh- water Biology" within the past year that the 

 amateur zoologist could hope to find even the names of 

 all the organisms which may be collected from a single 

 pool of water. And in many cases he will still meet with 

 disappointment, for many of our protozoa and other 

 fresh-water organisms have not yet been described as 

 species. 



During the past few years there has been a tendency on 



