. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. INHIBITION OF NEMATOCYST DISCHARGE 197 inhibition of stenotele discharge. Animals fed to repletion have a fully extended gastral cavity. Four hours later, shortly before regurgitation of the remaining food, the volume of the gastric cavity had returned close to that of a one-day starved animal, yet the animal killed very few of the offered shrimp; that is, stenotele discharge was still inhibited to a large degree. If simple physical dis- tention of the body wall were related to inhibition of stenotele discharge, we would hav
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. INHIBITION OF NEMATOCYST DISCHARGE 197 inhibition of stenotele discharge. Animals fed to repletion have a fully extended gastral cavity. Four hours later, shortly before regurgitation of the remaining food, the volume of the gastric cavity had returned close to that of a one-day starved animal, yet the animal killed very few of the offered shrimp; that is, stenotele discharge was still inhibited to a large degree. If simple physical dis- tention of the body wall were related to inhibition of stenotele discharge, we would have expected the extent of stenotele discharge, we would have expected the extent of stenotele discharge to be more like that of a starved animal than like a repleted one. 15 1 12 Q. E i_ co 01 .Q E --o--. _L _L 10 20 30 40 Time after decapitation (min) 50 60 FIGURE 4. Decay of inhibition of stenotele discharge in severed heads. At each time interval after severance, a group (3-5) of hydra were offered 15 shrimp and the number killed within two minutes noted. The two curves are for heads of repleted animals (filled circles) and for heads of starved animals (open circles). A related possibility concerns "neck formation" in the animal. Some time after feeding to repletion, the portion of the body column directly beneath the ring of tentacles elongates, that is, stretches, becoming very narrow like a neck (Blanquet and Lenhoff (1968). A stretch receptor located in this region could monitor ingestion and hence be involved in the control of nematocyst discharge. How- ever, this is unlikely because neck formation takes place after inhibition of steno- tele discharge sets in. Since physical distention of the body walls is probably not involved, the inhibi- tion of stenotele discharge may be due to the accumulation of a specific metabolite somewhere in the animal or to a general osmotic effect due to the accumulation of ions and metabolites in the gastral cavity. If so, gradual
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