Exochromic

There is no necessity for regarding some eyes as »exochromic«, and others as »autochromic«, since there is no evidence to show that pigmented mesoderm cells have forced their way through the basal membrane into the eye;

If my views as to the pigment cells are correct, the first formation of pigment by the cells of the vesicle and the later intrusion of the pigment cells from the mesoblast indicates that the present exochromic eye of Julus was derived from an earlier autochromic eye.

It has been known for ten years (owing to the work of Geddes and others) that another species of Convoluta (C. schultzii) contained chlorophyll, but whether the chlorophyll is autochromic, that is a product of the animal's activity; or exochromic, and due to symbiotic unicellular algæ, is a question which can scarcely be considered as thoroughly settled.