The mesogloea in the hydropolyp is a thin elastic layer, in which may be lodged the muscular fibres and ganglion cells mentioned above, but which never contains any connective tissue or skeletogenous cells or any other kind of special mesogloeal corpuscles.
Mesogloea of the medusa is largely developed and of great thickness in the umbrella.
The mesogloea is greatly developed in them and they are often of very tough consistency.
The ectoderm is indicated by close hatching, the endoderm by light hatching, the mesogloea by thick black lines, the horny skeleton of the pneumatophore and sail by dotting.
Between the ectoderm and endoderm a gelatinous supporting layer, termed the mesogloea, makes its appearance.