1920] Metcalf: Diptera 189 



Any one of the stages may be adapted for hibernation; perhaps 

 more often the pupa, then larva, adult and egg in the order 

 named. 



There are many curious mating habits among the Diptera. 

 A common habit is to pair while dancing in swarms. In several 

 cases the males emerge a little earlier and then await the emer- 

 gence of the females, as in Simuliidae and Tipulidae. Indeed, 

 the tipulid male is said to assist the female from the puparium. 

 Oestrid males await about the host animal for the approach 

 of the females. Secondary sexual ornaments of dolichopodid 

 males are displayed before the females; while certain Empididae 

 construct frothy balloons to attract the females. In the 

 Syrphidae I have noted mating while hovering, (both facing 

 the same way, male uppermost), and while resting on leaves, 

 facing in opposite directions. In the latter case it may continue 

 uninterruptedly for two or three days {Temnostoma spp.) 



In methods of reproduction we find a very great range. 

 Parthenogenesis seems not to have been developed in this 

 order. Ordinarily, fertilized eggs are laid in the usual way. 

 The Sarcophagidae are all larviparous or ovoviviparous. The 

 eggs hatch in utero and the active larvae are extruded, in this 

 family often being attached to a grasshopper or other host while 

 both insects are in flight. The number of offspring per female 

 in this family appears to be very high. 



In the Glossina and Hippoboscidae we find a remarkable 

 condition, analogous to the vivipary in mammals, in that the 

 larvae derive all the nourishment for their growth and develop- 

 ment from special glands in the uterus of the female. This, of 

 course, reduces greatly the potential number of offspring; there 

 are only six or eight per generation in the sheep tick. 



Another remarkable condition known as paedogenesis is 

 described for Miastor of the Cecidomyidae. It is said that eggs 

 are produced in ovary-like organs of the larva. These hatch 

 and the young larvae remain in the abdominal cavity feeding 

 on larval parent tissues until they finally escape. A series of 

 such multiplications is followed by pupation and a normal 

 sexual reproduction of adults. The pupa of a species of 

 Chironomus also reproduced parthenogenetically, according to 

 Grimm. 



