PREFACE TO THE THIRD EDITION. 



THE favor with which the first and second American editions of 

 Hertwig's Zoology have been received has led to a thorough revision 

 of the whole with a close comparison with the latest German edition. 



In this there have been introduced many new features bringing 

 the work up to date. These include a discussion of Mendelian inherit- 

 ance, many modifications in the account of the theory of evolution, 

 and a considerable enlargement of the Protozoa and especially of the 

 pathogenic forms, making the volume of more value to the student of 

 medicine. 



To have included these without changes elsewhere would have 

 resulted in a much larger volume. But the demand in American colleges 

 has been for a smaller work and so a reduction has been made in two 

 ways. There has been a condensation by the elimination of unnecessary 

 words and phrases and by the omission of considerable matter of minor 

 importance. Then there has been the recognition of the fact that the 

 book has two uses, one in the class room the other as a reference work. 

 The two classes of matter have been distinguished by differences of type. 



No attempt has been made to bring the systematic names into accord 

 with the latest vagaries of the systematists. No useful and could be 

 served by changing or transferring the well-known names of Echidna, 

 Coluber, Amia, Homarus, Unio, Holothuria, Amoeba, etc., while the 

 confusion this would introduce would be enormous. 



It should be understood that while the revision is based upon the 

 German edition of Professor Hertwig, he should not be held responsible 

 for any changes introduced. The whole responsibility for these rests 

 upon the American reviser. 



J. S. K. 

 TUFTS COLLEGE, MASS., June, 1912. 





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