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In the Cyclopidae the posterior antennae have lost their secondary branch, and the mandibles have completely thrown off the previously existing natatory feet, whilst in the other families these appendages persist, more or less altered.
Or to the organs of circulation? We have among the Copepoda, the Cyclopidae and Corycaeidae without a heart, side by side with the Calanidae and Pontellidae with a heart. And in the same way among the Ostracoda, the Cypridinae, which I find possess a heart, place themselves side by side with Cypris and Cythere which have no such organ. Or to the respiratory apparatus?
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