64 Journal New York Entomological Society, t'^'o-- x>^ix, 



subject separately; and the following discussion is therefore offered 

 as the first of such a series of papers dealing with the more important 

 features of value in the study of arthropodan evolution. 



It is extremely difficult for anyone who is not a specialist in the 

 Crustacea to obtain specimens of the rarer forms for dissection, and 

 on this account, it has been necessary for me to depend upon the 

 descriptions of others for the morphological details of certain of the 

 rarer Crustacea such as the Euphausiacea. Anaspidcs, etc., but I have 

 been fortunate in being able to examine representatives of these 

 forms, and I have been able to dissect other types sufficiently close to 

 these to enable me to form an opinion as to their relationships — and 

 luckily, those types of Crustacea which are of the greatest importance 

 for a study of the phylogeny of insects, are obtainable from the 

 biological laboratories of Europe. 



I would use this opportunity of expressing my very sincere grati- 

 tude to Miss Rathbun for the loan of a specimen of Anaspidcs and 

 other interesting material from the U. S. National Museum, and to 

 Dr. Caiman of the British Museum for specimens of the interesting 

 crustacean Apseudes. Dr. Chamberlin of the Harvard Museum has 

 furnished me with interesting and valuable myriopodan material, and 

 Dr. Walcott of the Smithsonian Institution has very generously given 

 me a number of photographs of trilobitan appendages, and has very 

 kindly allowed me to copy Fig. i8 (Plate VII) from his restoration 

 of the appendages of the trilobite Ncolcnus. I am also deeply in- 

 debted to Dr. Raymond of the Harvard Museum for much valuable 

 information concerning the affinities of trilobites; and Fig. 9 (Plate 

 VI) is based upon a restoration of the trilobite Triarthriis made by 

 him. 



General Considerations. 



It is indeed astonishing that so little attention has been given to 

 the evolution of the members of the phylum Arthropoda, since no 

 other group of living things can equal or even approach them in the 

 number of their species, in the multiplicity of their modifications of 

 structure and habit, or in their preservation of synthetic types serv- 

 ing to connect the various subdivisions of the group. The survival 

 of ancient types but little modified from their primitive condition, 

 such for example as Apns, which has changed but little since Cam- 



