Quarterly Journal of Microscopical Science, Vol s3-100, 445-462, Copyright © 1959 by Company of Biologists

The Ontogeny and Comparative Anatomy of some Protocerebral Sense Organs in Notostracan Phyllopods

¹ Zoological Institute, Lund

1. An investigation of the ontogeny of some of the protocerebral sense organs of Triops was carried out.

2. Attention is called to the presence of a frontal proliferation zone of great importance in the growth of the nauplius and compound eyes.

3. With respect to the nauplius eyes it is shown that to the small tripartite nauplius eye present at hatching additions are contributed partly by the dorso-lateral lobes of the brain, partly by the proliferation zone. This complicated mode of derivation of the nauplius eye is reflected in the arrangement of the nerves. The so-called upper lateral nauplius eye nerve in Triops is shown to be the remnant of the connexion between the nauplius eye and the ganglion opticum of the compound eye, and the evidence suggests that it is not really to be regarded as an optic nerve of the nauplius eye.

4. It is shown that the proliferation zone is mainly or exclusively responsible for the formation not only of the distal part of the compound eye but also of the ganglion layer of the lamina ganglionaris and of the distal part of the ganglion layer of the medulla.

5. The dorsal paired frontal organs as described by Claus (1873) are identified with a group of sensory cells situated above the lateral nauplius eye in the adults of Triops, and the ontogenetical processes involved in their dislocation are traced.

6. The group of cells in the neighbourhood of the ganglion opticum supposed by Wenke (1908) and Hanstrom (1931) to be identical with the frontal organs found by Claus (1873) probably constitute a neurosecretory organ.

7. It is shown that despite great topographical differences the ontogeny of the protocerebral sense organs of Artemia in many respects follows the same pattern as in Triops.