The Development of the larval and adult mid-gut of Calandra oryzae (Linn.): The Rice Weevil

Abstract

(i) Embryonic. 1. The blastodermal stage of insects corresponds to the blastula stage of other animals. 2. The primary yolk-cells are a secondary feature of the developing insect egg. 3. The ventral groove corresponds to the invagination of the gastrula. 4. The endodermal cells of insects are budded off into the yolk from the walls of the ventral groove or from thickenings in the blastodermal wall. 5. The endodermal cells in C. oryzae and most pterygota do not give rise to any larval or imaginal structures. 6. The larval mid-gut epithelium in C. oryzae and most pterygote insects is derived from the inner ends of the stomodaeum and proctodaeum and is therefore of ectodermal origin. 7. The accessory alimentary cell-mass present in the larva of Calandra oryzae is developed from the rudiments of the larval mid-gut epithelium. (ii) Post-embryonic. 8. The metamorphosis of the mid-gut in C. oryzae begins about three days before the pupal moult occurs. 9. The larval mid-gut epithelium collapses and degenerates. 10. The replacement cells take no part in the formation of the mid-gut of the adult. 11. The adult mid-gut epithelium in Calandra oryzae and five other Rhynchophorus species is derived from the posterior end of the metamorphosing fore-gut, and is therefore of definite ectodermal origin. 12. The accessory alimentary cells are incorporated in the walls of most of the mesenteric caeca. 13. The presence of the accessory cell-mass has nothing to do with the ‘Calandra’ type of formation of adult mid-gut epithelium. 14. The number of the accessory cells is reduced during imaginal life. 15. In insects with the ‘Calandra’ type the ‘yellow body’ contains no remains of the larval mid-gut epithelium. Such remains characterize the ‘Ptinus’ type, and differentiate it from that of Calandra. 16. The ‘Ptinus’ type probably is the more primitive.