Flagellates of Naegleria gruberi have an interconnected flagellar apparatus consisting of nucleus, rhizoplast and accessory filaments, basal bodies, and flagella. The structures of these components have been found to be similar to those in other flagellates. The development of methods for obtaining the relatively synchronous transformation of populations of Naegleria amebae into flagellates has permitted a study of the development of the flagellar apparatus. No indications of rhizoplast, basal body, or flagellum structures could be detected in amebae. A basal body appears and assumes a position at the cell surface with its filaments perpendicular to the cell membrane. Axoneme filaments extend from the basal body filaments into a progressive evagination of the cell membrane which becomes the flagellum sheath. Continued elongation of the axoneme filaments leads to differentiation of a fully formed flagellum with a typical "9 + 2" organization, within l0 min after the appearance of basal bodies.

Amebae of Naegleria gruberi transform into flagellates whose basal bodies have the typical centriole-like structure . The amebae appear to lack any homologous structure, even during mitosis . Basal bodies are constructed during transformation and, in cells transforming synchronously at 25°C, they are first seen about 10 min before flagella are seen . No structural precursor for these basal bodies has been found . These observations are discussed in the light of hypotheses about the continuity of centrioles .

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The formation and regulation of the larval lateral line melanophore band of Brachydanio rerio was investigated. It is comprised of about 30 melanophores linearly arranged along the horizontal skeletogenous septum. This stripe forms in two distinct stages, an initial migration and orientation of pigment cells which outlines the stripe, and a later round of melanophore differentiation which regulates and perfects the stripe. From the initial melanoeyte population which appears between approximately 24 to 48 hours of development and spreads ventrally over the body, some (0-21) melanocytes migrate to and reorient into the horizontal skeletogenous septum. At day 3 this initial lateral line stripe varies in melanophore number between individuals and even between left and right sides of the same embryo. By eight days of age however the lateral line bands of different fish are more uniform in appearance due to the entry of a second wave of melanophores which appear between days 4 and 8.Some observations suggested the operation of a cell territorial-regulating mechanism. Second round melanophores tend not to appear in somite areas already occupied by 3-day cells but invariably appear in unoccupied locations. We propose that some "exclusion principle" operates in this embryonic cell population, controlling the positions along the stripe where second wave melanophores can appear.The developmental phenomena which transform an immature, unpigmented animal into a juvenile or adult bearing a specific pigment pattern have been the subjects of much investigation (Dushane, '35; Twitty, '36, '45, '66; Twitty and Bodenstein, '39, '44; Lehman, '53; Mayer, '70; '74). It is now well documented that in the major classes of vertebrates, part of the cell population which migrates from the neural crest becomes localized in response to both intrinsic and extrinsic developmental cues to form species-specific pigment patterns (for a review of the neural crest and its derivatives see Weston, '70).The zebrafish, Brachydanio rerio, has provided excellent material for studies of pigment pattern development (Goodrich and Nichols, '31; Goodrich et al., '54; Thumann, '31; Shephard, '61; Kirschbaum, '75 ple, consisting of five alternating blue-black and silvery-yellow stripes aligned parallel to the long axis of the body ( fig. 1). This pattern extends onto both the caudal and anal fins, but not onto the dorsal or paired lateral fins where the pigmentation is diffuse and relatively unorganized. This simple stripe pattern is the culmination of a series of discrete developmental events, the first of which is the differentiation and migration of melanocytes which contribute to the 3-day pigmentation pattern. This early melanocyte pattern consists of four stripes: (1) the dorsal band, a double row of melanophores situated above the brain and spinal cord and extending from the head to the tail, (2) one lateral band, which consists of a row of melanophores along each side of the body and situated in the horizontal skeletogenous septum, the groov...