816 



AN INTRODUCTION TO ENTOMOLOGY 



BB. AntenriEe with circumfili or {Winnertzia) with horseshoelike appendages; 

 the first segment of the tarsi shorter than the second p. Si/.Cecidomyiin^ 



Subfamily LESTREMIIN^ 



The members of this subfamily differ from other gall-gnats in 

 having ocelli, in the shape of their eyes, these resembling those of 

 Sciara (Fig. 1029), and in the less reduced venation of their wings, 

 vein M being preserved ; in some genera this vein is forked (Fig. 1035) 

 in others it is unbranched. 



yl/i+2 



Fig. 1035. — Wing of Lestremia. 



(After Kiefifer.) 



Most of the known larvae of this subfamily live in decaying vege- 

 table matter, especially in rotten wood under bark. 



Subfamily HETEROPEZIN^ 



This subfamily includes comparatively few species, none of which 

 is known to be of economic importance. The known larva live in the 

 decaying bark of trees. Some of them are remarkable for the fact 

 that they give birth to living young. 



This type o^ reproduction is termed paedogenesis (See page 192). 

 It was first discovered by Nicholas Wagner in 1862 and has been in- 

 vestigated by several other Europeans. It has also been studied in 

 this country by Dr. Felt ('11) who gives an extended account of it as 

 observed by him. in Midstor americdna, and by Professor Hegner ('12 

 and '14) who gives the history of the germ cells in the psedogenetic 

 larva of this species. 



The larva of Miastor americdna possesses two ovaries, one on 

 either side of the body in the tenth or eleventh segments. Each ovary 

 consists of typically thirty-two oocytes, each of which is accompanied 

 by a group of nurse-cells, and with them is surrounded by a folicular 

 epithelium. The nuise-cells furnish nutrition to the growing oocytes, 

 gradually becoming reduced as the oocytes increase in size. Finally 

 the oocyte with accompanying nurse-cells, still surrounded by the 

 follicular epithelium, becomes separated from the rest of the ovary and 



