REGENERATION IN ISOLATED AND FUSED PIECES OF CLAVA LEPTOSTYLA l NORMAN E. KEMP Department of Zoology, University of Michigan, Ann Arbor. Micliii/an, and Mt. Desert Island Biological Laboratory, Salisbury Core, Maine Modern experimental studies on regeneration in hydroids, as Peebles (1931) anticipated, have been aimed at elucidating the factors responsible for this dramatic morphogenetic response. It is well known (reviews of Child, 1929, and Barth, 1940a) that coelenterate hyclranths exhibit axial gradients of metabolic activity and that distal levels exert dominance over proximal levels. Barth (1938b) demon-strated that in Tubularia circulation within the gastrovascular cavity is responsible for the maintenance of dominance, for if an isolated stem was ligatured hydranths might regenerate at both ends. The same result was attained if circulation in the coelenteron was blocked with an oil droplet (Barth, 1938b), with a bubble of oxygen or nitrogen or by means of an inserted glass rod (Rose and Rose, 1941). A series of recent papers have considered certain extrinsic factors affecting regeneration. Temperature (Moog, 1941) and the level of oxygen supply (Barth, 1938a, 1940b, 1944; Goldin, 1942b; Miller, 1937; Rose and Rose, 1941)' have been shown to be important in Tubularia. Accumulation of metabolic wastes (Rose and Rose, 1941 ; Miller, 1942) or lowered pH (Goldin, 1942a, 1942b) prevent regeneration. Zwill-ing (1939) showed that hydranths could be elicited along the side of a stem of Tubularia by cutting a window through the perisarc, thereby exposing the coenosarc directly to sea water, and Goldin and Barth (1941) have investigated the reorgani-zation of coenosarcal fragments free of perisarc. As background for further work on the physiology of regeneration, the present paper deals with the potentialities for regeneration revealed in isolated or fused pieces of hydranths of Clava leptostyla Agassiz. Papers by Hargitt (1906 and 1911) contain valuable descriptive infor-mation on this species and a more recent paper by Brien (1943) reports experi-ments on regeneration in a related species, Clava sqnainata. MATERIALS AND METHODS During the summer of 1950 Clava leptostyla was found to be abundant on the Fucus attached to rocks in the intertidal zone at Salisbury Cove, Maine. Clava grows in the form of colonies of separate light orange hydranths ( Fig. 1 ) attached to a mat of hydrorhiza firmly adherent to the substratum. Mature polyps, which are about 1 cm. in length when expanded, consist of a contractile stalk, a gonosome, tentacle-bearing region, and hypostome. The gonosome is a region possessing sev-eral short, branched gonophores bearing clusters of spherical sporosacs, which are either male or female. There is no free medusoid generation ; instead a planula 1 Aided by a grant from the Horace H. Rackham School of Graduate Studies, University of Michigan, and an Ulric Dahlgren Memorial Fellowship, Mt. Desert Island Biological Laboratory.. 141
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