Note 136 — Chapter XIII

It has long been known that land and freshwater forms develop without a metamorphosis much more frequently than marine forms. This is probably to be explained by the fact that there is not the same possibility of a land or freshwater species extending itself over a wide area by the agency of free larvæ, and there is, therefore, much less advantage in the existence of such larvæ; while the fact of such larvæ being more liable to be preyed upon than eggs, which are either concealed, or carried about by the parent, might render a larval stage absolutely disadvantageous.