In Crickets and Cockroaches and possibly other insects that eat solid food the mouth opens into a crop which opens into the proventriculus.
This is part of the fore gut is derived from an invagination of the external cuticle and as such has the potential to form hard spines.
Imagine a peeled orange with its segments intact but with a hollow center and an opening at the top and at the bottom. In this cricket there are 6 segments. The outer wall is muscular; the inner walls contain a whole array of spines. These spines break up solid particles into finer particles before they are passed into the mid gut.
Top view, BHS 4x DPlan objective, shows the inside of the proventriculus split open and laid flat on a slide; temporary glycerine mount.
2nd image, with SPlan 10x
3rd image, DPlan 20x
bottom ZS stereo of the 20x image
(images look better as large .tiffs)



