It is well known that in various phytoflagellates one of the flagella is connected with the eye-spot or stigma. In the case of Chromulina psammobia the more differentiated structure of the eye-spot+ flagellum complex seems analogous to that of a retinal rod with its connective cilium binding the external segment and the cell-body.

It is tempting to draw a parallel between this finding of comparative cytology and a hypothesis on the origin of Metazoa proposed first by J. R. Baker, and subsequently by A. C. Hardy.

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