52. The Anatomy and Histology of the Alimentary Canal in the Common Wasp (Vespa vulgaris).

Summary.

• 1
  The mouth-parts of the wasp are designed for biting, licking, and mastication; they are well developed in all castes; their musculature is fully described and compared with larva, and also with the bee and Dytiseus.
• 2
  The pharynx is a large sac with complicated muscles designed for pumping and swallowing. The elasticity of chitin is used to antagonize certain muscles; it co-operates with others, and these show reduced size.
• 3
  Certain direct homologies of larval and adult muscles are defined, and the significance of this possibility discussed.
• 4
  The esophagus and crop are typical.
• 5
  The proventriculus is well developed and acts as a pump in conjunction with the pharynx.
• 6
  The ventriculus is typical and is built upon a definite, geometric pattern which conditions the features seen in sections cut in known planes. The replacement cells are few and lie within the basement-membrane; any idea that they exist external to this is due to confusing them with a layer of fine longitudinal muscle-fibres whose presence confirms White's record of a third layer of ventricular muscles.
• 7
  The peritrophic membrane arises by “delamination,” probably as the result of condensation of cell-secretions, and not from the striated border nor the esophageal valve. It may represent a partially chitinous intima of the mid-gut.
• 8
  The small intestine has two well-marked histological areas and a local anterior muscle concentration acting as a sphincter or as a means of hastening peristalsis.
• 9
  The Malpighian tubules show well-marked secretion phases.
• 10
  The rectum has a general syncytium, with characteristic rectal pads. The interpretation of these structures awaits the further study of their development.
• 11
  The intrinsic muscles of the gut are attached to the basement-membrane lying below the digestive epithelium.