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

Abstract

Summary. 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. 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. Certain direct homologies of larval and adult muscles are defined, and the significance of this possibility discussed. The esophagus and crop are typical. The proventriculus is well developed and acts as a pump in conjunction with the pharynx. 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. 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. 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. The Malpighian tubules show well‐marked secretion phases. The rectum has a general syncytium, with characteristic rectal pads. The interpretation of these structures awaits the further study of their development. The intrinsic muscles of the gut are attached to the basement‐membrane lying below the digestive epithelium.