Uinc. IQ2I.1 Crami'ton: Hvull'tion of Tin: Antiipopoua. 67 



liiramous limb, clearly shows that they have not traced the modifica- 

 tions of the moiithpart limbs in a series of Crustacea leadinjj up to 

 the insectan ty])c, in order to give an intelligent opinion in the matter; 

 and the attempt of Wood-Mason, 1879. to homologize the incisor 

 process of the mandible of Machilis with the exopodite of a crus- 

 tacean limb, and to homologize the molar i)rocess of .\facliilis' 

 mandible with the endopodite of a crustacean liml), well illustrates to 

 what flights of fancy one may be led if he docs not take the precau- 

 tion of studying t'-~ modifications met witli in the Crustacea and 

 lower insects, hefore indulging in speculations concerning the in- 

 terpretation of the structures of insects in terms of crustacean 

 anatomy I Furthermore, the fact that an entomologist of the reputa- 

 tion of Folsom. 1900, should suggest that the mandibular palpi of 

 Crustacea represent the exopodites of crustacean limbs, very clearly 

 indicates (in addition to the other instances cited above) that en- 

 tomologists in general are not sufticiently familiar with the develop- 

 mental tendencies exhibited by Crustacea and other forms related to 

 lower insects, to enable them to correctly analyze the conditions met 

 with in lower insects. On this account. I have devoted the greater 

 part of the present discussion to an attempt to trace the evolution of 

 the mandibular appendage in those arthropods which approach the 

 insectan type, instead of taking up the consideration of the evolu- 

 tion of the mandibles within the class Insecta — which I am hoping 

 to discuss in a future publication on this subject. 



Origin' of Artiiropodax Appendages. 



The lines of descent of the Arthropoda arc ap])roache(l by those 

 of the Onychophora, Tardigrada, Myzostomida and ' Annelida"; but 

 the lines of the descent of the Onychophora. Tardigrada and Myzos- 

 tomida lead off toward paths of specialization which do not parallel 

 that of the arthropods very closely, and the condition occurring in the 

 appendages of these forms (see textfigures 9, 10, and 11 ) does not 

 throw much light upon the subject of the nature of tiie precursors of 

 arthropodan limbs, although a study of the condition found in the 

 groups in question is not wholly without value. On the other hand, the 

 amielids approach the arthropods in so many i)articulars. that I am more 

 inclined to seek the ty|)e of structure foresliadouing an arthropodan 



