"Two female sporosacs (degenerate medusae) of Hydraetinia echinata. a, ectoderm; b, endoderm; o, eggcella; g, entric cavity. In A an invagination of the ectoderm, which is more complete in B, represents the rudiment of the sub-umbrella space." — Encyclopedia Britannica, 1893

Sporosac

"Two female sporosacs (degenerate medusae) of Hydraetinia echinata. a, ectoderm; b, endoderm; o, eggcella;…