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In the Ostracoda, Zenker describes a gland situated in the base of the inferior antennae, and opening at the extremity of an extraordinarily long "spine." The adherent feet are retracted within the rather opaque anterior part of the shell. Pupa of Sacculina purpurea, magnified 180 diam.
The Copepoda, the Ostracoda, and the Branchiopoda are the Crustacea which have departed least from the embryonic or Nauplius-forms; and, of these, I imagine that the Copepoda represent the hypothetical Archicarida most closely. Apus and Sapphirina indicate the relations of these Archaeocarids with the Trilobita, and the Eurypterida connect the Trilobita and the Copepoda with the Xiphosura.
How well warranted are we therefore in identifying the latter with the former. Equally scanty is our knowledge of the developmental history of the Ostracoda. The development of Cypris has recently been observed by Claus: "The youngest stages are shell-bearing Nauplius-forms." The section of the Branchiopoda includes two groups differing even in their development, the Phyllopoda and the Cladocera.
The Crabs and Macrurous Crustacea, the Stomapoda, the Diastylidae, the Amphipoda and Isopoda, the Ostracoda and Daphnidae, the Copepoda and Parasita, the Cirripedes and Rhizocephala of our coast, representing the class of Crustacea with the deficiency only of the Phyllopoda and Xiphosura, furnished a long and varied, and at the same time intimately connected series, such as was at my command in no other class.
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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