DEVELOPMENT AND FUNCTION OF NEUROSECRETORY SITES IN THE EYESTALKS OF LARVAL PALAEMONETES (DECAPODA: NATANTIA)

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Abstract
The histogenesis of neuro-haemal structures is essentially the same in P. kadiakensis, P. pugio, P. vulgaris, P. intermedius and P. paludosus. The sensory pore X-organ can be seen 5 days before hatching as a vacuole close to the outer surface of the eyestalk. Onion bodies develop between the vacuole and the ganglionic mass. At hatching, a giant cell appears between the medulla terminalis and the m. interna. This cell appears to become active during the first zoeal stage. It is suggested that the giant cell is the source of stainable material in the SPX. At metamorphosis, the eyestalk rotates on its longitudinal axis. This results in the maintenance of the orientation of the sensory pore with the substrate, while the rest of the animal assumes the dorsal-side-up position of the adult. The sinus gland does not become functional until after metamorphosis. Apparently the migration of neurosecretory substances from the brain and thoracic ganglia does not begin until post-larval life. The ganglionic X-organs of the adult are not functional during larval development. Eyestalk removal had no effect on larval molt cycles or on metamorphosis, but resulted in complete paleness of the larval shrimp. It is suggested that endocrine systems operating in Palaemonetes larvae differ in several respects from those of the adult.