vi pbMface. 



PREFACE TO THE SECOND EDITION. 



Besides a number of minor corrections, this edition has 

 been, it is hoped, improved by the addition of four brief 

 chapters, with illustrations, relating to the centipedes, etc. 

 {Myriopoda), the spiders (Arachnida), the net-veined in- 

 sects without, and those with, a complete metamorphosis, 

 representing several of the smaller orders of the class Insecta. 

 Additional sections on the ctenophores, and on the horse- 

 shoe crab and its allies the trilobites {Podostomata), have 

 also been inserted. 



Providbnce, July, 1887. 



PREFACE TO THE FIFTH EDITION. 



The chief changes made in the present edition are three : 

 first, the transfer of the chapter on Bchinoderms to follow 

 the chapter on Worms, since the former now appear to have 

 been derived from some worm-like form, and agree in some 

 details of structure with, and are on nearly the same plane of 

 organization as, the higher worms. The second change is 

 in the arrangement of the orders of Crustacea, the Branchi- 

 opoda being now regarded as the earliest and most general- 

 ized group. The third change is the addition of lists of and 

 references to the most authoritative text-books and treatises 

 both on general zoology and the special classes, and it is 

 hoped that both teachers and pupils will use such works, 

 many of which are well illustrated, for reference or study. 



Provipence, May 36, 1893. 



