STUDIES ON THE HEXAPOD NERVOUS SYSTEM. VI. VENTRAL NERVE CORD SHORTENING; A METAMORPHIC PROCESS IN GALLERIA MELLONELLA (L.) (LEPIDOPTERA, PYRALLIDAE)

¹ Department of Entomology and Parasitology, University of California, Berkeley 4, California

1. Gross features of interganglionic connective shortening during metamorphosis of Galleria mellonella (L.) are described. Gradations range from no significant shortening, to partial shortening, to shortening with establishment of contiguity between ganglia, to complete shortening with coalescence of ganglia.

2. Under the experimental conditions employed, shortening commences about a day prior to ecdysis, and is completed 30-45 hours after ecdysis. The rates at which various connectives shorten differ significantly from one another. If linearity is assumed, these range from 0.3 to 0.5 mm. per day.

3. Much of the shortening is compensated by subsequent elongation of connectives. The two morphogenic processes are not in phase; shortening is 70-75% complete before elongation can be detected.

4. The adult ventral nerve cord is about 15-20% shorter than that of the stage I larva from which it has developed. Shortening has altered the relative locations of certain of the ganglia so that they are in accord with structural reorganization of the skeleto-muscular system. Not only are ganglia retained close to their effector organs as a consequence, but conduction times between certain of the centers would be expected to be reduced.