PSYCHE. 



THE MOUTH PARTS OF THE NEMATOCEROUS DIPTERA,— I. 



BV VERNON L. KELLOGG, STANFORD UNIVERSITY, CALIFORNIA. 



The repeated attacking of the prob- 

 lem of the homologies of the mouthparts 

 of the Diptera will result in giving us, 

 sometime, a solution. The problem is 

 not inherently insoluble. It is to be 

 solved as other problems in homology 

 have been solved and are daily being 

 solved, namely, by a study of the com- 

 parative anatomy and a study of the 

 ontogeny or development of the organ 

 or organs in question. But any such 

 study of homology has inevitably to do 

 with more than the mere determination 

 of homologies : it is inevitably a study 

 of phylogeny. 



There are two phases of the work of 

 the student of phylogeny : comparative 

 anatomical study and ontogenetic or 

 developmental study. The study of 

 comparative anatomy includes not only 

 the study of the living members of the 

 group in hand, but also the study of the 

 extinct members, the paleontologic 

 phase. As any organism is simply 

 the sum of its organs, it follows that 

 the phyletic study of a group of organ- 

 isms resolves itself into a phyletic study 

 of the body organs, and the phylogeny 

 of any one of these organs, fully and 



correctly worked out, is a great step 

 toward revealing the phylogeny of the 

 group of organisms. For the descent 

 of an organ is synchronous with the 

 descent of an organism. 



The determination of the homologies 

 of an organ or group of organs through- 

 out a group of organisms involves the 

 discovery of the primitive, racial, most 

 generalized condition of the organ in 

 the group, and then the various kinds 

 of specialization the organ e.xhibits, and 

 the paths from generalized to special- 

 ized condition for each of these kinds 

 of specialization. This is no more nor 

 less than true phyletic study. 



The problem presented us, then, in 

 the homologies of the dipterous mouth; 

 parts, so often attacked and in such 

 various ways, seems to me plainly a 

 phyletic problem, and to be solved most 

 expeditiously, if not only, by the rational 

 and accepted methods of systematized 

 phylogenetic investigation. The com- 

 parative anatomy of the mouthparts of 

 the living flies (the paleontologic phase 

 of the work is in this case impossible), 

 is to be studied with the aim of deter- 

 mininn; what is the most generalized 



