25, C) to the inner face of the vesicle, thus forming the mesoblast.
8); the primitively open cup has now closed over to form a vesicle lying beneath the ectoderm; the outer wall of the vesicle becomes thickened to form a cellular lens (1), while the proximal wall consists of sensory and pigmented cells and forms a retina.
M, The water - pore, leading by the stone - canal stc to the waterring, from which hangs a Polian vesicle pb.
Bergh (for Lumbricus and Criodrilus), whose figures show a derivation of the entire nephridium from mesoblast, and an absence of any connexion between successive nephridia by any continuous band, epiblastic or mesoblastic. A midway position is taken up by Wilson, who asserts the mesoblastic formation of the funnel, but also asserts the presence of a continuous band of epiblast from which certainly the terminal vesicle of the nephridium, and doubtfully the glandular part of the tube is derived.
It contains a closed vesicle regarded by Schepotieff as a right probosciscavity and in any case representing the pericardium of Balangolossus, the glomerulus of which is also probably represented.