Short Appendages Research Articles

Thismia taiwanensis sp. nov. (Burmanniaceae tribe Thismieae): First Record of the Tribe in China

A new holomycotrophic species, Thismia taiwanensis (Burmanniaceae), is described and illustrated from Kaohsiung County, south-central Taiwan. It most closely resembles the Japanese species T. abei and T. tuberculata, but is distinct as the flowers are subsessile, the outer surface of the perianth tube is smooth, the outer tepals bear very short solitary appendages, and the inner tepals bear longer solitary appendages. This represents the first record of both Thismia and Burmanniaceae tribe Thismieae in China. The genus Thismia Griff. (Burmanniaceae) consists of ca. 35 species of small holomycotrophic herbs, typ- ically growing amongst leaf litter on the forest floor. The only comprehensive taxonomic monograph of the genus was published by Jonker (1938), who recognized 23 species in Thismia itself, as well as several other genera that have been subsequently reduced to syn- onymy with it, viz. Glaziocharis Taub. ex Warm. (one species), Triscyphus Taub. ex Warm. (one species), Geomitra Becc. (one species), and Scaphiophora Schltr. (two species). Jonker (1938) proposed a supraspecific classification system for Thismia, with five sections. This classifica- tion was necessarily reassessed following the accep- tance of a broader generic concept for Thismia: Hatu- sima (1976), for example, established Thismia sect. Gla- ziocharis (Taub. ex Warm.) Hatusima following the re- duction of Glaziocharis into synonymy with Thismia. Maas et al. (1986) recently proposed a comprehensive subgeneric and sectional classification for the neotrop- ical members of the genus, with several new taxa that were previously recognized as distinct genera. Although Thismia has an essentially pantropical distribution, several species have been described from warm temperate regions. In Asia, the genus extends northwards into southern Japan: T. abei (Akasawa) Ha- tusima (syn. Glaziocharis abei Akasawa) has been re- corded from Honshu, Shikoku, and Kyushu (Akasawa 1950; Shin 1974, as ''Glaziocharis sp.''; Matsumoto and Yamada 1994), and T. tuberculata Hatusima has been recorded from Kyushu (Shin 1974; Hatusima 1976). A new species of Thismia was recently collected in Kaohsiung County in south-central Taiwan; this rep- resents the first record of the genus in China. The spe- cies is formally named and described here as T. tai- wanensis S.-Z. Yang, R. M. K. Saunders & C.-J. Hsu. T

New species of Autolytus Grube, 1850, Paraprocerastea San Martín & Alós, 1989, and Sphaerosyllis Claparède, 1863 (Syllidae, Polychaeta) from the Iberian Peninsula

During the project Fauna Iberica, established to develop a complete inventory of Iberian fauna, several new species belonging to the family Syllidae Grube, 1850 were found. In this paper, Autolytus labordai n. sp., Paraprocerastea draculai n. sp., and Sphaerosyllis parabulbosa n. sp. are described. Autolytus labordai n. sp. is characterized by having long nuchal lappets, short appendages, relatively long blades on the compound chaetae, and a trepan composed of eight or nine large teeth separated from one another by two medium-sized teeth or by two medium-sized teeth with one small tooth between them. Paraprocerastea draculai n. sp. is characterized by having tapering and somewhat flattened antennae, tentacular cirri and dorsal cirri of chaetiger 1, and short and ovoid dorsal cirri on the remaining parapodia. Its trepan is composed of two large, fang-shaped teeth, separated by two semicircles of 12-14 smaller teeth. Lastly, it only possesses simple chaetae, of which those of the anterior two chaetigers a...

Taxonomy of the South American genus Pachypops Gill 1861 (Teleostei: Perciformes: Sciaenidae), with the description of a new species

Pachypops is a South American freshwater sciaenid genus characterized by having two anal-fin spines, three mental barbels, an inferior mouth, a swimbladder with a pair of short appendages anteriorly and a pair of longer appendages projected posteriorly, and the haemal spine of the first caudal distinctly expanded. Three valid Pachypops species are recognized herein. Of the six nominal species previously assigned to Pachypops, two are herein recognized as valid (Perca fourcroi and Micropogon trifilis), two are assigned to other sciaenid genera (Pachypops adspersus and Pachypops cevegei) and two are considered junior synonyms (Corvina biloba and Pachypops camposi). A seventh nominal species, Pachyurus nattereri, formerly considered a valid species of Pachyurus, is determined to be a junior synonym of Pachypops fourcroi, and lectotype and paralectotypes are designated for it. Pachypops fourcroi occurs in the Orinoco, Amazonas, Essequibo, Corantijn, and Approuague River basins, and Pachypops trifilis in rivers of Guyana and middle and lower reaches of the Rio Amazonas basin. A third valid species, Pachypops pigmaeus n. sp., is herein described from tributaries of the Rio Amazonas, Brazil.

MOLECULAR BIOGEOGRAPHY OF CAVE LIFE: A STUDY USING MITOCHONDRIAL DNA FROM BATHYSCIINE BEETLES

This study focuses on phylogenetic relationships in two distinct species assemblages of cave-dwelling beetles with similar disjunct distributions in the Pyrenees and Sardinia. One assemblage contains six species in the genera Ovobathysciola (four species) and Patriziella (two species) on Sardinia and one species of Anillochlamys in the Pyrenees. Species within the two Sardinian genera co-occur in the same karst area. Although, they are believed to be each others closest relative, they have very different body types (globular body with short appendages in Ovobathysciola; elongated body with long appendages in Patriziella), which are believed to reflect different degrees of adaptation to cave life. The other assemblage of Bathysciine beetles includes three species in the genus Speonomus in the Pyrenees and one on Sardinia. All the species are rare and many are endangered.One issue of particular interest was whether Ovobathysciola and Patriziella are reciprocally monophyletic or whether each of the Patriziella species evolved independently from the co-occurring Ovobathysciola species, as the similar morphology of the Patriziella species might be due to convergence rather than common descent. Based on DNA sequences of the cytochrome oxidase I (COI) region of the mtDNA, neither scenario was supported. Rather, the two Patriziella species are sister taxa embedded within the Ovobathysciola radiation. In addition, the well-dated geological history of this region allowed us to calibrate absolute rates of COI evolution, the first such estimates for any insect. Finally this study suggests that the evolutionary acquisition of typical cave adaptations (e.g., elongated body and appendages) may occur at about the same rate as loss of traits (e.g., eyes and pigmentation) associated with cave life.Corresponding Editor: E. Zouros

Molecular biogeography of cave life: a study using mitochondrial DNA from bathysciine beetles.

This study focuses on phylogenetic relationships in two distinct species assemblages of cave-dwelling beetles with similar disjunct distributions in the Pyrenees and Sardinia. One assemblage contains six species in the genera Ovobathysciola (four species) and Patriziella (two species) on Sardinia and one species of Anillochlamys in the Pyrenees. Species within the two Sardinian genera co-occur in the same karst area. Although, they are believed to be each others closest relative, they have very different body types (globular body with short appendages in Ovobathysciola; elongated body with long appendages in Patriziella), which are believed to reflect different degrees of adaptation to cave life. The other assemblage of Bathysciine beetles includes three species in the genus Speonomus in the Pyrenees and one on Sardinia. All the species are rare and many are endangered. One issue of particular interest was whether Ovobathysciola and Patriziella are reciprocally monophyletic or whether each of the Patriziella species evolved independently from the co-occurring Ovobathysciola species, as the similar morphology of the Patriziella species might be due to convergence rather than common descent. Based on DNA sequences of the cytochrome oxidase I (COI) region of the mtDNA, neither scenario was supported. Rather, the two Patriziella species are sister taxa embedded within the Ovobathysciola radiation. In addition, the well-dated geological history of this region allowed us to calibrate absolute rates of COI evolution, the first such estimates for any insect. Finally this study suggests that the evolutionary acquisition of typical cave adaptations (e.g., elongated body and appendages) may occur at about the same rate as loss of traits (e.g., eyes and pigmentation) associated with cave life.

Utriculimermis microcaudata n. gen., n. sp., a new genus and species of Mermithidae (Nematoda) of the rivers Lafnitz and Teigitsch in the southeastern Austrian Alps

AbstractUtriculimermis microcaudata n. gen., n. sp. (Nematoda: Mermithidae) is described from the hyporheic biotope of two running waters in southeastern Austria. The mermithids were sampled by pumping and with a modified 'Hess'-sampler. The characteristics of this new genus are: long body length, a very long pharynx which attains about 95% of the body length, six head papillae, mouth opening terminal, six hypodermal chords at midbody level, excretory pore present near the nerve ring, small cupshaped amphids, cuticula lacking cross fibres under light microscope, males with long slightly curved spiculum, very large number of genital papillae, vulva slightly curved to barrel-shaped with vulval flap, postparasitic juveniles with very short tail appendage often only present as a button-like nipple.

Taxonomic Studies on the Genus Marssonina in Korea

Eight species of Marssonina parasitic on 21 species of host plants from Korea are described and illustrated. They are Marssonina brunnea (Ellis & Everh.) Magnus, M. capsulicola (Rostr.) Magnus, M. celastri H.D. Shin & H.T. Lee, M. coronaria (Ellis & Davis) Davis, M. fragariae (Lib.) Kleb., M. juglandis (Lib.) Magnus, M. rosae (Lib.) Died, and M. sennenis (Gonz. Frag.) Vassiljevsky & Karak. Of these, M. capsulicola and M. coronaria sometimes poss three-celled conidia and M. sennenis is characterized by a short appendage at the basal end of the conidia. Morphological features of conidia and host ranges were of taxonomic values for species delimitation.

Three New Brazilian Species in the Genus Marcetia (Melastomataceae, Melastomeae)

Three new species of Marcetia are described and illustrated. Marcetia semiriana occurs only in Serra do Cip6, Minas Gerais. Marcetia shepherdii, collected in Marai1, at sea level, and M. lychnophoroides, from Chapada Diamantina, are both endemic to Bahia. The new species Marcetia shepherdii and M. lychnophoroides, together with M. luetzelburgii Markgraf, constitute a group of closely related species. They share in common subcoriaceous, fleshy, imbricate to subimbricate, revolute leaves. Marcetia shepherdii is distinguished by its rigid, erect branchlets, yellowish green leaves that are glabrous on the adaxial surface, unappendaged and broadly dilated connectives, linear-oblong thecae with a ventrally inclined pore, and a unique 2locular ovary. Marcetia lychnophoroides has velutinous to sublanate branchlets, cinereous-green leaves that are densely puberulous-sericeous on the abaxial surface, unprolonged and inconspicuously bilobulate connectives, and a 3or 4-locular ovary. Marcetia semiriana is very similar to M. taxifolia (A. Saint-Hilaire) DC., differing in the prostrate branches, long pedunculate flowers, and straight anthers. Marcetia is a neotropical genus of 27 species largely endemic to Brazil. Except for the widespread Marcetia taxifolia, which has a bicentric distribution in eastern Brazil and northwestern South America (Colombia, Venezuela, and Guyana), all other species of Marcetia have restricted distributions. Marcetia species are usually shrubs or subshrubs that occur in campo rupestre in the Serra do Espinhago, Minas Gerais, in the mountains of Goi s, and especially in the Chapada Diamantina, Bahia. Campo rupestre is an exclusively Brazilian complex mosaic of vegetation types characterized by extensive outcrops of highly acidic rocks, nutrient-poor soils, and local variations in topography, slope, aspect, and moisture regime. A few Marcetia species occur in both montane and littoral areas, such as M. ericoides (Sprengel) 0. Berg ex Cogniaux and M. canescens Naudin. Marcetia shepherdii is the only species in the genus that is endemic to coastal Bahia, where it occurs in the sandy vegetational formation commonly referred to as restinga. The genus Marcetia can be distinguished within the tribe Melastomeae mainly by the combination of tetramerous flowers and simple anthers that lack basally prolonged connectives (except in M. shepherdii) and, in some species, may have short ventral tuberculate appendages. Three of the species studied in my taxonomic revision of Marcetia (Martins, 1989) are new. They are described and illustrated here. Marcetia shepherdii A. B. Martins, sp. nov. TYPE: Brazil. Bahia: Maraui, 4 km de Mara6, 12 Mar. 1977 (fl, fr), G. J. Shepherd, L. S. Kinoshita, J. B. Andrade & N. Taroda 4550 (holotype, UEC). Figure 1. Haec species Marcetiae luetzelburgii affinis, sed ab ea foliis arcte adpressis sessilibus revolutis dense imbricatis internodia brevia occultantibus, ramis basin versus denudatis, conspicue annulis foliorum delapsorum praeditis, lamina foliari supra glabra in sicco flavovirescenti, staminum filamentis ter longioribus, antheris apice rotundato ventraliter minute dehiscenti atque ovario biloculari differt. Erect subshrub ca. 60 cm, compactly branched; branchlets rigid, subterete to inconspicuously quadrangular, moderately puberulous or nearly glabrous, at the base defoliating with age and with conspicuous leaf scars. Leaves opposite, sessile, appressed, densely imbricate and concealing the short internodes; blade lanceolate-ovate, 2.5-3 x 1 mm, fleshy-coriaceous, basally cordate, apically recurved and mucronulate, margins revolute, glabrous on the adaxial surface, glandular-pubescent abaxially, obscurely 1-nerved. Flowers 4-merous, subsessile, solitary in upper leaf axils resembling a terminal foliaceous spiciform inflorescence, becomNOVON 10: 224-229. 2000. This content downloaded from 157.55.39.45 on Fri, 02 Sep 2016 06:22:09 UTC All use subject to http://about.jstor.org/terms Volume 10, Number 3 2000 Luckow & Du Puy Gagnebina bakoliae from Madagascar 225

Seasonal morphometric variation in sexual and asexual, North American and Australian, populations of the aphid, Acyrthosiphon pisum

SummaryThe lengths of the body and appendages of the aphid Acyrthosiphon pisum (Harris) (Homoptera: Aphididae) vary seasonally in sexual North American and asexual Australian populations. The first generation of spring aphids in North America and winter aphids in Australia have short appendages in relation to body length. Excluding this phenotype, North American and Australian aphids cannot be discriminated morphometrically. The short appendages in North America are associated with a specialized morph called a fundatrix; the short appendages of Australian aphids are caused by exposure to low temperatures during prenatal development. The same temperature‐sensitive mechanism operates in sexual and asexual North American aphids, but does not explain the short appendages of the fundatrix, which appear to arise through a separate mechanism. The short appendages are caused neither by a maternal effect from winged mothers, although such an effect exists, nor by seasonal changes in body length and allometry, nor by microevolutionary changes. The temperature‐induced shortening of appendages is a seasonal polymorphism, which mimics the short appendages seen in fundatrices. The two types of phenotypic plasticity have the same consequence in sexual and asexual populations of the same species and may be an example of convergent evolution.

Morphological Variation of the Green Toad, Bufo viridis, in Italy: A Test of Causation

Morphological Variation of the Green Toad, Bufo viridis, in Italy: A Test of Causation

Cell-Contact-Stimulated Formation of Filamentous Appendages by Salmonella typhimurium Does Not Depend on the Type III Secretion System Encoded by Salmonella Pathogenicity Island 1

The formation of filamentous appendages on Salmonella typhimurium has been implicated in the triggering of bacterial entry into host cells (C. C. Ginocchio, S. B. Olmsted, C. L. Wells, and J. E. Galán, Cell 76:717-724, 1994). We have examined the roles of cell contact and Salmonella pathogenicity island 1 (SPI1) in appendage formation by comparing the surface morphologies of a panel of S. typhimurium strains adherent to tissue culture inserts, to cultured epithelial cell lines, and to murine intestine. Scanning electron microscopy revealed short filamentous appendages 30 to 50 nm in diameter and up to 300 nm in length on many wild-type S. typhimurium bacteria adhering to both cultured epithelial cells and to murine Peyer's patch follicle-associated epithelia. Wild-type S. typhimurium adhering to cell-free culture inserts lacked these filamentous appendages but sometimes exhibited very short appendages which might represent a rudimentary form of the cell contact-stimulated filamentous appendages. Invasion-deficient S. typhimurium strains carrying mutations in components of SPI1 (invA, invG, sspC, and prgH) exhibited filamentous appendages similar to those on wild-type S. typhimurium when adhering to epithelial cells, demonstrating that formation of these appendages is not itself sufficient to trigger bacterial invasion. When adhering to cell-free culture inserts, an S. typhimurium invG mutant differed from its parent strain in that it lacked even the shorter surface appendages, suggesting that SPI1 may be involved in appendage formation in the absence of epithelia. Our data on S. typhimurium strains in the presence of cells provide compelling evidence that SPI1 is not an absolute requirement for the formation of the described filamentous appendages. However, appendage formation is controlled by PhoP/PhoQ since a PhoP-constitutive mutant very rarely possessed such appendages when adhering to any of the cell types examined.

Development and fine structure of murine Purkinje cells in dissociated cerebellar cultures: neuronal polarity.

Cerebellar Purkinje cells (PC) display a highly distinctive form of polarity. We have cultured murine PCs from dissociated E16 cerebellar anlagen for 1 week to investigate the early stages of neuronal compartmentalization and synaptic interactions, features which are important for the establishment of neuronal polarity. To unequivocally identify the PCs we utilized light and electron microscopic immunocytochemistry with an anti-serum to the cell class-specific marker L7/pcp2 gene product. The PCs typically show a single, long axon, numerous short appendages classified as filopodia and protospines, and a small number of protodendrites. The nucleus is positioned asymmetrically in both the horizontal and vertical axes of the soma. The Golgi apparatus, coated and uncoated vesicles, and mitochondria are prominent ultrastructural features, while the endoplasmic reticulum is highly fragmented. The cell body receives rudimentary synapses on its smooth surfaces and appendages and no consistent morphological differences were detected between these elementary contacts. The axon is clearly identifiable; it emanates from either the cell body or a protodendrite, bifurcates at predominantly right angles, forms beaded collaterals, and terminates with relatively large growth cones. The varicosities of the PC axon contain pleomorphic synaptic vesicles and form rudimentary synapses primarily with the dendritic shafts of immunonegative neurons. The protodendrites are short, quickly tapering and sparsely branched; they emit numerous filopodia and immature spines and terminate with small growth cones. Rudimentary synapses are received on the proximal dendritic shafts and filopodia, and more mature synapses occur frequently on protospines. With few exceptions, PCs lie atop an astrocytic bed layer and glial processes are apposed to the various aspects of the PC body left free by the afferent axons. By contrast, PC processes are largely free of glial sheaths. We conclude that the "stellate stage" of PC development in situ is replicated rather faithfully in culture and that PCs have established polarity and have begun to form intercellular contacts by 1 week in vitro. Moreover, the PCs are already morphologically distinct from other cell types in the 1 week cultures, although they have yet to develop the differentiated features that distinguish mature PCs.

Afferents from the colliculus, cortex, and retina have distinct terminal morphologies in the lateral posterior thalamic nucleus

We have examined the morphology of afferent endings that originate in three distinct cell groups and terminate in the lateral posterior nucleus of the thalamus (LP). Retino-LP projections were sparse, occurred throughout the nucleus, and could be classified into 1) simple en passant varicosities and terminal swellings found on poorly branched fibers in all LP subdivisions, 2) string-like configurations of varicosities detected largely in the medial subdivision of the LP, and 3) terminals resembling retinogeniculate endings occurring mainly in the rostral part of the superficial subdivision of the LP adjacent to the dorsal nucleus of the lateral geniculate body. Cortico-LP terminals fell into three classes: 1) single varicosities decorating the tips of short appendages on fine preterminal and terminal axons; 2) tiny, round varicosities studding the axon shaft; and 3) boutons of variable shape visible on medium-caliber corticothalamic fibers. Tecto-LP terminals exhibited a large variation in morphology and density. Those found most commonly could be classified into two groups: 1) individual swellings and 2) terminal clusters arranged in a tubular configuration that enclosed a central channel, most likely occupied by the dendrite of a postsynaptic neuron. An unusual tecto-LP terminal consisted of an ovoid swelling (up to 20 microns in the long axis) from which emerged several long, thin extensions and was seen at the tips of large-diameter axons. These results show that, despite having overlapping projection zones, each set of afferents that projects to the LP elaborates terminal specializations that are structurally distinct from others projecting to the same target area.

Afferents from the colliculus, cortex, and retina have distinct terminal morphologies in the lateral posterior thalamic nucleus

We have examined the morphology of afferent endings that originate in three distinct cell groups and terminate in the lateral posterior nucleus of the thalamus (LP). Retino-LP projections were sparse, occurred throughout the nucleus, and could be classified into 1) simple en passant varicosities and terminal swellings found on poorly branched fibers in all LP subdivisions, 2) string-like configurations of varicosities detected largely in the medial subdivision of the LP, and 3) terminals resembling retinogeniculate endings occurring mainly in the rostral part of the superficial subdivision of the LP adjacent to the dorsal nucleus of the lateral geniculate body. Cortico-LP terminals fell into three classes: 1) single varicosities decorating the tips of short appendages on fine preterminal and terminal axons; 2) tiny, round varicosities studding the axon shaft; and 3) boutons of variable shape visible on medium-caliber corticothalamic fibers. Tecto-LP terminals exhibited a large variation in morphology and density. Those found most commonly could be classified into two groups: 1) individual swellings and 2) terminal clusters arranged in a tubular configuration that enclosed a central channel, most likely occupied by the dendrite of a postsynaptic neuron. An unusual tecto-LP terminal consisted of an ovoid swelling (up to 20 μm in the long axis) from which emerged several long, thin extensions and was seen at the tips of large-diameter axons. These results show that, despite having overlapping projection zones, each set of afferents that projects to the LP elaborates terminal specializations that are structurally distinct from others projecting to the same target area. J. Comp. Neurol. 388:467–483, 1997. © 1997 Wiley-Liss, Inc.

Seiridium papillatum, a New Species (Mitosporic Fungus) Described on Stems of Eucalypts in Australia

A second species of Seiridium is described on Eucalyptus spp. in Australia as S. papillatum sp. nov. It is distinguished from the known species of the genus by its short papillate conidium appendages and large, ellipsoid to sub-cylindrical, striate, 5- (4–7-) septate conidia. A key to S. papillatum and closely related Seiridium species is provided and morphological differences are discussed. Colony morphology and growth rate of S. papillatum at different temperatures are compared with those of S. eucalypti and a Seiridium isolate from Callitris.

A new variety of Myxotrichum ochraceum from Japanese soil

Myxotrichum ochraceum var.frigidum, a new variety ofMyxotrichum, is described and illustrated from the material from Japanese soil. It is morphologically characterized by dull green to black ascomata with a yellow-orange centrum, peridium consisting of a fragile hyphal network, peridial hyphae with internal coiled branches and short spine-like appendages, pale yellow fusiform striate ascospores, and the absence of an anamorph. The new variety primarily differs from the type variety in the absence of elongate appendages. A key to all accepted species of the genus is revised.

Phylogeny and biogeography of the Niphargus transitivus group of species (Crustacea, Amphipoda)

The Niphargus transitivus group includes 12 groundwaterdwellingspecies. It is defined by an upright body position during locomotion,a small, stout body with short appendages, except for long coxae and dactyli, coxae V-VI equilobate or posterolobate, accessory flagellum subject to reduction, and the body endowed with adaptations for volvation (= ability to enroll into a ball).

M ring, S ring and proximal rod of the flagellar basal body of Salmonella typhimurium are composed of subunits of a single protein, FliF

The flagellar basal body, a major part of the flagellar motor, consists of a rod and four rings. When the fliF gene of Salmonella typhimurium, which was previously shown to code for the component protein of the M ring, was cloned and overexpressed in Escherichia coli, the FliF subunits formed ring structures in the cytoplasmic membrane. Electron microscopic observation of the purified ring structures revealed that each was composed of two adjacent rings and a short appendage extending from the center of the rings. Antibodies raised against the purified FliF protein decorated both the M and S rings of the intact basal body. We conclude that the FliF protein is the subunit protein of the M ring, and of the S ring and of part of the proximal rod of the flagellar basal body.

The Business Ethic of the World Religions and the Spirit of Capitalism

Ten years after the publication of "The Protestant Ethic and the Spirit of Capitalism" Weber presented the social sciences with an ambitious series of essays on the "Business Ethic of the World Religions." This series was cut short by his untimely death in 1920. As it stands it includes a study of Confucianism and Taoism, Buddhism and Hinduism, ancient Judaism, and a short appendage on the Pharisees. It was his intention to supplement the study of ancient Judaism with an analysis of the Psalms and the Book of Job. Treatises on Talmudic Judaism, the Islam, and early Christianity had been outlined and would have completed this extensive piece of research had he been able to continue his work.

Dendritic maturation of displaced putative cholinergic amacrine cells in the rabbit retina

The dendritic trees of Cb, cholinergic, amacrine cells in the ganglion cell layer of the developing rabbit retina are revealed by intracellular injection with Lucifer yellow to have the adult dendritic branching pattern at birth. It is demonstrated that these cells maintain a constant number of dendritic branches throughout postnatal development and that their dendritic trees increase in size by the growth and subsequent elongation of all branches. Proximal and distal dendrites increase in length by almost the same proportions between birth and adulthood. Although the adult pattern of dendritic branching of Cb amacrine cells is established by birth, dendrites in the young possess numerous short appendages (1-5 microns in length) resembling the "dendritic spines" of immature cat retinal ganglion cells. Some of these structures remain on the dendrites of adult cells but the majority are lost at the end of the third postnatal week. As dendritic spines disappear, the dendrites of Cb amacrine cells, especially the distal portion of the tree, acquire numerous varicosities. At each stage after P10, the gain in the number of varicosities greatly exceeds the loss in spines; this is not consistent with the hypothesis that all varicosities are retracted dendritic spines. The rapid increase in the number of varicosities on distal dendrites of Cb amacrine cells during the first 3 postnatal weeks coincides with the maturation of amacrine cell physiological responses. There is no distinct centroperipheral gradient in the postnatal dendritic maturation (acquisition of varicosities, loss of spines, attainment of the adult number of branches) of Cb amacrine cells from the visual streak to the peripheral retina. However, the area of their dendritic tree increases relatively more in the retinal periphery compared to that in the visual streak.