REVISER’S NOTE. 
In revising the work of Professor Orton, the writer has 
not attempted to rewrite the book nor to introduce new 
ideas.' His plan has been to insert such changes as the 
author would have been likely to make if he had lived to 
revise his book. On only two points has the reviser de¬ 
parted from this plan of altering only minor details. The 
chapter on Development has been largely rewritten, and 
the classification of the Invertebrates has been changed 
so as to separate the worms from the Arthropoda and 
the sponges from the Protozoa. In both these cases the 
change seemed imperatively demanded by the progress of 
Zoology in those directions. It is hoped that the altera¬ 
tions in the book will increase its accuracy and useful¬ 
ness. 
Edw. A. Biege. 
University of Wisconsin. 
