Sensory Cells and Pigment Distribution in the Tail of the Ammocoete

The ammocoete of Lampetra planeri (Bloch) contains a single carotenoid, lutein, partly esjerified and partly in the free state. The pigment is distributed in lipophores in the sub-dermal tissues, and plays no part in the colour changes of'the animal. The epidermis of the tail contains numerous sensory cells of a type previously undescribed, which satisfy the requirements predicted for the photoreceptors responsible for the light reaction of the animal. Evidence is presented that these sensory cells are innervated by branches of the lateral line nerves. Similarities are indicated between the sensory cells of the ammocoete and simple photoreceptor systems of certain invertebrates.