BOTH THE SEXES IN DIPTERA. 377 



and one not capable of extrusion ; while the male, as I have shown in Tabanus bromius, 

 has complex genitalia. 



Nearly identical conditions are found in the Culicidse. 

 Cases where the genitalia are complex in both sexes : — 



2. The male lias very complex, though not complete, genitalia in Tipula oleracea, 

 and the female a striking ovipositor. The mouth-parts are comparatively simple, the 

 mandibles being fused into the labium ; the galeae of the maxillae and the labial palpi 

 are absent; the labrum and hypophar^'nx are very imperfect; the tracheae of the 

 paraglossae are not well-developed, and the whole organ seems to have undergone great 

 changes. Jn the Muscidse the genitalia are quite as complex, and we find nearly the 

 same armature on the mouth, except that the palpi are labial and not maxillary. 



Cases where the mouth-parts are nearly aborted : — 



3. In Gastrop'dus equi the mouth-parts consist only of an aperture and two hairy 

 processes. The compensation in this case seems to be in size, as the ovipositor is a very 

 prominent part of the insect, and the genitalia of the male are large and chitinous. 



Cases where the genitalia incline towards simplicity : — 



4. JParydra coarctata has comparatively simple genitalia, the spinus and palpi 

 genitalium being absent. The mouth-parts are proportionately very large ; a distinct 

 clypeus (which I have submitted is the true labrum) is present, and the structure of the 

 tracheae is abnormal. 



Case where the genitalia is simple in mechanism but well-developed as to size : — 



5. In Empis stercorea, whose genitalia I have already commented on, the mouth- 

 parts are large, the labium, maxillae, hypopharynx, and labrum well-developed and 

 strong, the only weak parts being the maxillary palpi. 



So-called teeth on Paraglossce : — 



1. In all cases where the ovipositor is of the Musca domestica type, the teeth on tlie 

 labella are thin and transparent, or absent. 



2. In all cases where the ovipositor has hardened, as in the Ortalidae and Lonchaeidae, 

 the teeth are quite absent. 



3. In most cases where the teeth are strongly developed, as in the Cordyluridae, the 

 ovipositor is short as in Scatophaga stercoraria (Linn.) (PI. 30. fig. 131) ; the exceptions 

 are in the Ccenosia group of the Anthomyzidae, where very chitinized teeth are found, 

 together with a long, membranous ovipositor. The males arc of the Muscid type, which 

 is complicated as a whole, but tends towards simplicity of the individual organs. 



Summarij as to the failure of parts in the male mouth. — From these cases it may be 

 assumed that when the male mouth-armature is failing or variable, it is brought about 

 by reason of a relationshiji between mouth and genitalia, the over-development of one 

 part causing, by compensation, the failure or simplification of the other. That being so, 

 the nature of the food in the blood-sucking species has no connexion with the failure 

 of the mouth of the male, though it may possibly have acted indirectly on the genitalia 

 bv reason of its stimulatino; character. 



The fact that in Slomo.rys, Hcematobia, or Glossina both sexes are blood-sucking and 

 identical in mouth-armature, supports this view, as the mouth-armature is, though 



