The Collaborative International Dictionary of English v.0.48:

Ventriculus \Ven*tric"u*lus\, n.; pl. Ventriculi. [L., belly,
   dim. fr. venter belly.] (Zool.)
   (a) One of the stomachs of certain insects.
   (b) The body cavity of a sponge.
       [1913 Webster]