96 Journal New York Entomological Society, t'^'o'- xxix, 



of tlie trilobite's mandibular limb, and the immediate differentia- 

 tion of its gnathobase into a highly complicated apparatus including 

 a specialized incisor region, a lacinia mobilis, a gnathofimbrium, and 

 a specialized molar process, involve too profound and far reaching 

 changes to be accomplished save by a gradual process of evolution 

 involving a long series of intermediate stages. 



9. The Crustacea not only approach the insectan type astonish- 

 ingly closely, but they also furnish us with a long series of inter- 

 mediate stages connecting the insectan types of structures with the 

 lower arthropodan forms, such as the Trilobita. Furthermore, they 

 not only furnish excellent connecting links between the Insecta and 

 lower arthropods, but they are the only forms which furnish these 

 intermediate types leading from the lower arthropods to the Insecta, 

 and this fact is one which cannot be ignored in attempting to de- 

 termine the character of the ancestors of insects. 



10. The Crustacea not only furnish the intermediate stages leading 

 from the lower arthropods to the insectan type, but they also furnish 

 us with the key to the proper interpretation of the homologies of the 

 various insectan structures, and they enable us to clear up many of 

 the false views concerning the meaning of the parts of the mandibles 

 as well as other structures of insects. Thus, a study of the evolution 

 of the mandibular appendage in the Crustacea clearly shows that the 

 incisor region, the lacinia mobilis, the gnathofimbrium and the molar 

 process are merely differentiated portions of the masticatory surface 

 of a gnathobase or endite, while a similar study of the appendages 

 homologous with the maxillc'e of insects indicates that the lacinia 

 represents a complete endite (or "gnathobase") of one segment of a 

 limb, while the galea represents a second endite of another segment 

 of the limb, whose terminal segments form the maxillary palpus. It 

 is thus impossible to homologize the lacinia mobilis of the mandible 

 with the lacinia of the maxilla in insects; and since the mandible 

 represent only one segment with its gnathobase, while the body of the 

 maxilla represents at least two segments with their endites (or 

 gnathobases) it is obviously incorrect to claim that the parts of the 

 maxilla are repeated in the mandible, as is done by many entomologists. 



11. A study of the mandibles, in connection with other features, 

 would indicate that insects arose from ancestors which were an- 



