MOULTING, GROWTH, AND SURVIVAL AFTER EYESTALK REMOVAL IN UCA PUGILATOR

¹ From the Marine Biological Laboratory, Woods Hole, Mass.

After removal of the eyestalks in Uca pugilator, all of the animals moulted within 35 days after the operation, and a few of the animals moulted twice within 48 days. Only 29 per cent of the normal animals moulted within 48 days, and none moulted twice. Eyestalk removal not only accelerated moulting but shortened the time in which the first and second moults occurred. The time at which the same percentage of moulting occurred was somewhat greater for non-segregated than for segregated animals.

Viability is related to moulting, and most of the deaths following eyestalk removal in this species are due in part to a mechanical difficulty and in part to some severe deficiency occurring during or aggravated by ecdysis. There is insufficient evidence to decide whether the eyestalks secrete a specific, life-sustaining hormone directly responsible for the continued life of the animal, or whether the viability effect is in some way dependent on the moult-inhibiting function of the eyestalk. We do not believe that the loss of the eyestalks per se is directly responsible for the total mortality seen in eyestalkless crabs because of the negligible percentage of deaths occurring from 1 to 5 weeks before moulting, and because operated animals live for 5 weeks without showing any external signs of serious debilities only to succumb after ecdysis. Seventy-five per cent of the total mortality can be related directly or indirectly to ecdysis, while 25 per cent (which includes the 10.5 per cent viable specimens) does not fall in this category and may be cited in support of a differentiation of the viability and moult-inhibiting functions of the eyestalk.

Eyestalk removal also leads to increased size. Some of the eyestalkless specimens 48 days after the operation have attained gigantic proportions. Pigmentation also seems to be lost, an effect which is noticeable after the first moult. No effect of eyestalk removal has been noted on copulation and shedding of eggs.