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The state of being made up of branchiate segments.

The absence of such renal caeca in Limulus and their presence in the terrestrial Arachnida is precisely on a parallel with their absence in aquatic Crustacea and their presence in the feebly branchiate Amphipoda.

Thus we see that in our aquariums most of the axolotls remain in the branchiate condition, transformed individuals being on the whole very exceptional.

But there is no reason to suppose that a congenital defect of thyroid arising as a mutation was the original cause of the neoteny, i.e. the peisistence of the larval or aquatic, branchiate condition.