BOTH THE SEXES IN DIPTEEA. 373 



Further Remarks on llie llelutionship between Genitalia 

 and Mouth-parts. 



In support of the idea that similar laws goveru the growth of the genitalia and the 

 mouth-parts, I have, in a tentative fashion, prepared a tahle of relationships, which gives 

 the parts of the male and female which have already been homologized in the previous 

 discussion, as well as a list of portions of the mouth-armature which, from structure or 

 function, appear to he the counterparts of the genitalia. In justification of this selection 

 I have some evidence which, taken by itself, might be treated as mere coincidence, but 

 gains weight from the other parts fitting into their places. 



Fulcrum or Suhm.entum. — In the mouth-parts of the Muscidge, embedded in the base 

 of the proboscis, is a chitinous plate which, from its median suture and lateral continua- 

 tions, is obviously a fusion of two organs. It is used to extrude and control the labium, 

 having attachments for many muscles. Lowne calls it the " fulcrum," and says * : 

 " Gerstfeldt t is, I believe, the only author who has anticipated me in the statement 

 that the maxillae enter into the composition of the fulcrum, but he merely observes, 

 ' The anterior lancet (labrum) shows distinctly, by the presence of a median raphe, that 

 it is formed of two halves, which must be the blades of the maxillae (Kieferladeu). 

 They rest upon a piece extending backwards (the fulcrum) which appears to be the 

 united stipites, from which two slender, nail-shaped parts diverge downwards and 

 backwards.' " 



I have called J the part the " submentum," which has been thought to be the cardines 

 and stipites of the second pair of maxillae (usually called the labivim), differing in this 

 from Lowne, who considers it to be the first pair of maxillae, because I have shown that, 

 together with this part (the fulcrum), there exist in Hydrellia griseola. Fall., nearly 

 complete first maxillie, and in identical situations in other Diptera these are nearly 

 always present, the stipites and cardines often carrying the maxillary palpi. 



Relation of the Great Apodeme to the Submentum. — The double apodemes, from their 

 situation below the theca, from their paired character, and from their function, I 

 consider to homologize with this part, the submentum or fulcrum. 



I have shown the double apodemes to be separate paii-ed organs in some species, in 

 others partially fused, the upper part being forked, and in other species totally fused. It 

 is remarkable how analogous this part seems to be with the submentum. 



* 'Blow-fly,' p. -133. 



t 'Ueber die ilundtheile der saugcndcn Insecton.' 8vo. Dorpat, 1853. 



X "The Labial and Maxillary Palpi in Diptera," Trans. Linn. Soe. Loudon, ser. II. Zool. vol. ix. (1903). 



54* 



