THE ANATOMY OF INSECTS. 43 



* like the oviducts unite and form an unpaired duct, the diictus 

 cjacnlatorius. Accessory glands open into this duct. 



All insects are developed from eggs. But there are some ap- 

 parent exceptions. Thus many flies retain their eggs till after they 

 are hatched, if a proper place for laying them is not found earlier ; 

 and in some flies (the Pupipara) the young attain a considerable 

 development before they are born. In the Plant-lice (Aphidida) 

 there is a remarkable alternation of reproduction by budding with 

 the sexual reproduction. 



