Branchiostoma lanceolatum larvae: some experiments on the effect of thiouracil on metamorphosis
Wickstead, J.H. (1967) Branchiostoma lanceolatum larvae: some experiments on the effect of thiouracil on metamorphosis. Journal of the Marine Biological Association of the United Kingdom, 47 (1). pp. 49-59.
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Larvae of Branchiostoma lanceolatum (Pallas), of a late pre-metamorphosis stage and characterized by a bright fluorescent green around the ilio-colonic ring, were taken in the Plymouth area plankton in August 1965. Adults were kept in 0'04 % thiouracil to determine the general effect at this concentration. It was lethal over a period of weeks. The larvae were kept in the dark at a constant temperature of roO C, individually or in pairs, in 0'04 %, 0'02 %, 0'01 %, 0'005 % and 0'0025 % thiouracil, in saturated solutions and suspensions of thyroxine and triiodothyronine, and in ordinary sea water. Solutions were changed weekly. The flagellate Dunaliella primolecta Butcher was supplied as food. All the larvae metamorphosed at approximately the same time and rate, two exceptions being that 0'04 % thiouracil was a more obviously toxic concentration and the thyroxine and triiodothyronine larvae were rather more precocious in their metamorphosis. It is suggested that metamorphosis is a 'triggered' process and is selfsustaining. Thus once it has begun it cannot be delayed or accelerated significantly. All the larvae caught were at a stage when this 'triggering' had been released. It is considered possible that the metabolism of the larva and the initiation of metamorphosis is controlled by a secretion of the club-shaped gland.
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