DIPTERA. 4 2 9 



wings (Fig. 500) is also very peculiar. All of the longitu- 

 dinal veins separate near the base of the wing except veins 

 III a and III 3 and veins V s and V 2 . In some forms veins 

 III 4 and III 6 are distinct, as shown in the figure ; in others 

 they coalesce completely, so that radius is only four-branched. 

 In this case there is only a single vein between the two 

 forked veins. 



The antennae are long and slender, and are clothed with 

 whorls of hairs (Fig. 501). Those of the male are longer; 

 and in the species figured the two 

 basal segments are clothed with scales 

 like those of the Lepidoptera. Scales 

 of this form occur also on the wings, 

 palpi, and legs of certain species. 



Only a few of the American species 

 have been described ; these have been 



Fin. 501. Antennfe of Psy- 



placed in the genus Psychoda ; the choda. m, antenna of male 



and the second segment of the 



early Stages of none of them have same more enlarged ;/, an- 



* tenna of female and the tip 



been observed. The larvae of some enlarged. 



European species inhabit cow-dung, and others live in water. 



They have a pair of spiracles at each end of the body. 



As regards the structure of their wings these flies are very distinct 

 from all others. The pre-anal area, that part lying in front of vein 

 VIII, presents an extremely generalized form. This is shown by the 

 outline of the wing (a line drawn lengthwise of the wing through its 

 centre will divide it into two similar parts), the small extent to which 

 the veins coalesce, and the fact that the maximum number of veins is 

 present. On the other hand, the anal area is so reduced as to be 

 barely represented. The dotted line in the figure represents the 

 position of what is left of the anal furrow (i.e., vein VIII). 



Family TlPULlD.-E (Ti-pu'li-dse). 

 The Crane-flies. 



The crane-flies are mosquito-like in form ; but they are 

 usually very much larger than mosquitoes. The body is 

 long and slender, the wings narrow, and the legs very 



