The Occurrence and Functional Characteristics of Heteromorph Antennules in An Experimental Population of Spiny Lobsters, Panulirus Argus*

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Abstract
1. Eyestalks were removed unilaterally from forty-nine Panulirus argus. Twenty-three of the forty-three animals remaining alive to the first moult regenerated a heteromorph antennular outer flagellum in place of the amputated eye. 2. None of the lobsters moulting within less than 3 months of eyestalk ablation regenerated a heteromorph; 70% of those moulting after more than three months recovery regenerated a heteromorph. If the heteromorph did not appear upon the first moult it usually continued to be missing after the second or third moult. 3. Mechanical stimulation of the heteromorph produced a general withdrawal reaction in all lobsters tested, and in most either a specific cleaning reflex directed toward the stimulated heteromorph, or a specific movement of the normal ipsilateral antennule, or both. The withdrawal and antennular movement, when it occurred, resembled responses elicited via stimulation of the normal antennular flagellum. 4. Behavioural responses were followed in a selected subpopulation for periods ranging from one to nearly two years, and over one or two moults. No significant changes in behavioural responses to heteromorph stimulation were detected within that time. 5. The conduction-velocity spectrum of fibres in the heteromorph nerve resembled that in the outer flagellar branch of the normal antennule nerve in having both a fast and a slow component. However, the velocity of the fast component of the heteromorph nerve was often less than normal for the flagellar branch of the antennule nerve, and additional components of intermediate velocity occurred in some animals. 6. According to the direction or nature of the mechanical stimulus both heteromorph and normal flagella elicited inhibitory and excitatory responses in the nerve to the depressor muscle of the outer flagellum of the normal ipsilateral antennule. 7. Responses of the flagellar depressor muscle of the ipsilateral antennule to electrical stimulation of the heteromorph varied among individuals, but in general resembled later components of the response to similar stimulation of the normal antennular flagellum.