ON THE PAIR OF SO‐CALLED SENSORY PITS OF THE NINTH ABDOMINAL SEGMENT OF THE WIREWORM (AGRIOTES OBSCURUS LIN.) WITH ADDITIONAL NOTES ON THE INTERNAL ANATOMY

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Abstract
Summary.: The structural evidence obtained from the study of the pits on the ninth abdominal segment of Agriotes obscurus favours the view that they are a pair of muscular impressions. The hairs lining the pit walls do not possess a nervous supply nor was any special nervous supply traceable to the pits as a whole. No structures which have been associated with sense reception in insects were found in the neighbourhood of the pits. There wm no evidence that the pits are a modified pair of spiracles as was suggested by one miter (6).With regard to the alimentary canal there are no salivary glands. The oesophagus possesses four ridges which project into its lumen and their muscular nature suggests that they are capable of independent movement.The mesenteron is devoid of gastric coeca and does not contain a peritrophic membrane of any type.The digestive fluid is secreted in vesicles which are budded off from the epithelial cells lining the midgut. The contents of the mesenteron has a pH of between seven and eight which is similar to the reaction of its cell walls. The hindgut is a straight tube without clearly marked intestinal and rectal regions and there are no glands of any kind in this part of the gut.The malpighian tubes are four in number and are generally of a yellow colour, but it is not unusual to find blackened patches in the tubes which are due to dark masses of excretory matter blocking the tube.The dorsal vessel is non‐septate.Besides the supra‐ and sub‐oesophageal ganglia there axe 11 nerve massea in the central nerve chain—three thoracic and eight abdominal.The masses of fat body are characterised by their leaf‐like shape and great length.

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