Fig. 10.

A proposed pathway of brood pouch formation in the seahorse. The pathway is schematically shown in both cross-sectional and sagittal views. a Before formation of the brood pouch. b The primordium of the brood pouch first appears as linear projections at both ventrolateral sides of the body. c The projections become fused at the body midline. d Differentiation of brood pouch tissue begins, and the pseudoplacenta first appears on the dorsal side of the pouch. e The pseudoplacenta eventually surrounds the pouch entirely. f Finally, the pouch-folds are formed, ready to incubate embryos. Dotted lines in sagittal views indicate locations of cross-sectional views. The typical developmental periods of the brood pouch stages and body length are given at the bottom of the figure. Formation may differ between individuals depending on rearing temperature and/or nutrition. a, anterior; d, dorsal; p, posterior; v, ventral