ZOOLOGY. 599 



attached the halteres or balancers ; only the two posterior 

 wings present; thelabium prolonged in to a proboscis, which 

 incloses the setiform maxillae. Larvae apodal and white. 



The Diptera resemble the Entozoa in a striking man- 

 ner through their apodal, soft and white larvae, and even 

 through their habitation, which is mostly in fetid and 

 moist animal matters. Added to this, they respire 

 usually through two tubes which open upon the anus. 



Many during their metamorphosis do not shed their 

 skin ; but it becomes, during the pupa condition, only 

 horny, representing a small case, whose bottom springs 

 up in front like an operculum, and gives exit to the 

 perfect Fly which has been therein developed. 



Upon the first abdominal ring of the iinago two 

 nodose pedicles stand out, which are called halteres ; 

 they are probably the old respiratory tubes. 



The maxillae have changed into bristles, which act like 

 pestels within the groove-shaped labium, puncture and 

 pump in the fluid. 



They divide into three families like the White-blooded 

 Worms, or according to the orders of their cohort. 



Fam. 1. Typical Diptera, Sckmeissen. 



Antennae triarticulate, the last joint being mostly 

 spatulate and furnished with a lateral awn or bristle; 

 only two suctorial setae inclosed between the terminal 

 valves of a fleshy proboscis, which admits of being re- 

 tracted within a large cephalic or oral cavity. The 

 Muscidae, unto whom the Common House-flies belong, 

 and also the Hippoboscidae or Louse-flies. It is my 

 opinion too, that the Fleas also are to be ranged among 

 the Diptera. 



Alliance 1. KlappenmucJcen. The two punctuating 

 setae placed between two valves without a proboscis 

 Flea (Pulex) and Louse-fly (Hippobosca.) 



Alliance 2. Acalyptera. Proboscis having thick lips, 

 and retractile into a large cephalic cavity ; alulae or 

 halteral opercula arrested Hypocera to Dolichocera. 



Alliance 3. Dung-flies. Characters similar to the 

 above, but the alulets are of considerable size Muscidae. 



