Morphology and histology of the alimentary canal in scorpionfly Panorpa obtusa(Mecoptera:Panorpidae)

The morphology and histology of the alimentary canal in the scorpion-fly Panorpa obtusa Cheng were investigated using light and scanning electron microscopy.In an antero-posterior direction,the foregut includes a pharynx,an oesophagus,and a proventriculus,but is devoid of crop.The elongate pharynx is subdivided into the anterior pharynx and the posterior pharynx or pharyngeal pump,which is inserted with dilator muscles.The proventriculus possesses numerous uniform brown proventricular acanthae on the sclerotized intima,performing the functions of filtrating,grinding,and temporarily storing food particles.Six cardiac valves protrude into the midgut.The long midgut is distensible with longitudinal muscles outside circular muscles;the epithelium consists of large columnar and small regenerative cells.There are no gastric caeca and peritrophic membrane.Six long brown Malpighian tubules are located at the junction between the midgut and the hindgut,extending freely into the heamocoel.The hindgut is subdivided into a V-shaped ileum,a loop-shaped colon,and a translucent,distensible rectum where six rectal pads are located alternatively.Finally,the structure and function of the alimentary canal and its significances in Panorpidae taxonomy are briefly discussed.