The structure and development of the digital lamellae of lizards

The epidermal setae and the spinules of the digital lamellae of anoline and gekkonid lizards are shed periodically along with the rest of the outer layer of the skin. These structures are developed within the lamellae prior to ecdysis. The setae are larger and more complicated than the spinules and begin their development first. The setae of Anolis start as aggregations of tonofibrils beneath the plasma membrane of the presumptive Oberhautchen cells. These cells are arranged in rows parallel to the surface, several cell layers beneath the alpha layer of the skin. The developing setae protrude into the clear layer cells as finger-like projections, with the tonofibrils longitudinally oriented in the direction of growth. About 100 setae are formed by each Oberhautchen cells in Anolis. In late development, the clear layer cells lose their cellular contents and when shed along with all distal cells, retain a template of the new setae or spinules. The spinules and setae are formed before the fibrous and alpha layers of the new skin. The fibrous layer, which occurs only on the ventral (outer) layer of the lamellae, and the Oberhautchen with its setae and spinules, is considered the beta layer. The alpha layer, which occurs adjacent to the fibrous layer on the ventral surface and adjacent to the Oberhautchen on the dorsal (inner) surface, is morphologically identical to that of mammalian α keratin. The shed lizard skin consists of the alpha and beta layers as well as the degenerating cells of the outer epidermal generation, and the clear layer. The clear layer that is shed shows the template of the new setae and spinules developed in the new skin layer. The separation of the new from the old skin occurs along the intercellular space between the clear layer cells and the new Oberhautchen. The alpha layer of the skin is not fully keratinized at shedding. The setae of the digital lamellae of lizards represent unique epidermal structures — intracellular keratinized microstructures.     

A whole lamella perspective on the origin of the epidermal free margin of Anolis (Reptilia: Dactyloidae) toe pads

Anoline lamellae terminate in an epidermal free margin carrying the majority of its setae. How the free margin is extruded from the body of the scale is not well understood. Two hypotheses have been advanced to account for it, one advocating distal migration of the outer epidermal layers relative to the body of the lamella, and the other proposing regression of the dermal core. Available evidence provides partial support for both. We assembled a series of specimens of Anolis grahami representing all shedding cycle stages, and prepared histological sections of the toe pads to allow measurement of appropriate lamellar components through the shedding cycle. Through its proliferative phases the lamellae increase markedly in length, with the distance between the distal tip of the dermal core and that of the lamella accounting for most of this, indicating that epidermal extrusion is responsible for production of the new free margin. The dermal core showed no evidence of regression. Concomitant with epidermal extrusion, the lacunar cells on the inner lamellar face hypertrophy and keep pace with the increasing thickness of the outer lamellar face resulting from the lengthening of the replacement setae. The integrated changes observed are consistent with continuity of functioning and alignment of the exposed setal carpet of the outer epidermal generation while ensuring that the new setal carpet is fully aligned and functional immediately after shedding. At shedding the original proportions of the lamellae are restored. Development of the new free margin results from a combination of distal displacement of Oberhäutchen cells along with arrested maturation of the epidermis in this region. Changes in length of the lamellae during the proliferative stages may impact the overall size of the adhesive toe pad, which may have consequences for assessments of the relationship between whole animal clinging ability and adhesive pad area. J. Morphol. 278:360–368, 2017. © 2017 Wiley Periodicals, Inc.     

Scanning electron microscopy of scales from different body regions of three lizard species

The Oberhautchen of scales from the dorsal, parietal, and ventral regions of Sceloporus occidentalis (Iguanidae), Gerrhonotus multicarinatus (Anguinidae), and Anniella pulchra (Anniellidae) were examined with a scanning electron microscope. At low magnification, all scales of S. occidentalis exhibit well-defined outlines of cells belonging to the Oberhautchen layer and the previously overlying clear layer. The dorsal and parietal cells of this species exhibit a minutely dentate Oberhautchen that forms tooth-like spinules 0.2 to 0.5 μ long and arranged in irregular rows. Minute pits 0.1 to 0.3 μ in diameter characterize the Oberhautchen of a ventral scale. Cell outlines are not evident on the scales of G. multicarinatus. The Oberhautchen of dorsal and parietal scales of this species is prominently laminated. Laminae are less prominent on scales of the lateral fold, and no intrinsic surface structure is evident on a ventral scale. In contrast, the fossorial anguinomorph Anniella pulchra exhibits Oberhautchen surfaces with practically no intrinsic microornamentation. However, what appear to be outlines of Oberhautchen cells are visible on the dorsal and ventral scales. These observations suggest that modifications of Oberhautchen microornamentation may have evolved to reduce friction with the substrate or other scales. The lack of pronounced microornamentation of the Oberhautchen on some body scales may indicate that a complex interdigitation between clear layer and Oberhautchen cells is not essential to the sloughing process.     

Ultrastructure of aesthetasc innervation and external morphology of the lateral antennule setae of the spiny lobster Panulirus interruptus (Randall)

Summary Six types of setae and one type of cuticular depression were examined on the lateral antennule of the spiny lobster Panulirus interruptus using scanning electron microscopy. The organization and ultrastructure of the innervation of the most numerous setal type, the aesthetasc, were investigated using light-and transmission electron microscopy.Each aesthetasc is innervated by approximately 300 bipolar neurons whose sensory dendrites penetrate the hair and extend toward the tip, and whose axons project towards the central nervous system. The neuronal somata and two types of glia form a cluster within the antennular lumen. The inner sheath-cell somata encircle the dendritic tract distal to the sensory somata. These cells appear to extend distal processes which wrap the dendritic tract to the base of the aesthetasc. Elongate outer sheath cells are interposed between the glia-wrapped dendritic tract and the hypodermis which underlies the antennule cuticle. A continuous investment of neural lamella separates the hypodermis, the entire cluster of somata, and sensillar nerve from the antennule lumen. The organization of the neuronal somata and their association with outer and inner sheath cells in this marine species appear similar to those of crustaceans from freshwater and terrestrial habitats.     

Root Anatomy and Mycotrophy of the Achlorophyllous Voyria tenella Hook. (Gentianaceae)

The central cylinder of the root of Voynet tenella consists of up to ten central, non-lignified, tracheidal xylem elements surrounded by some parenchymatic tissue and 5–7 groups of phloem. A pericycle could not be discerned. Even though the endodermis carries a faint suberin lamella it cannot be discerned anatomically without special staining. The cells of the 1–3 cortex layers next to the endodermis are elongated longitudinally, the subsequent cortex parenchyma is multi-layered and consists of isodiametric cells. The cells of the 2–3 layered outer dermal tissue are smaller than those of the adjacent cortex, their walls carry a suberin lamella and the outermost of them constantly scale off. The dermal tissue is interpreted as a multilayered exodermis. The fungal colonization in roots of Voyria tenella remarkably differs from any known mycorrhizal pattern. After having penetrated the dermal tissue, the always intracellularly-growing hyphae head straight towards the inner cortex layers, where they spread along the central cylinder. Ramifications from these inner-spreading hyphae then colonize the cortex parenchyma from the inside and they develop dense hyphal coils. Eventually, the coiled hyphae swell and collapse, resulting in amorphous clumps of fungal material. This mycorrhizal pattern is referred to as an intraradical fungus garden. Arguments are given to call the mycorrhiza in Voyria tenella a specialized arbuscular mycorrhiza. Phylogenetic and ecological implications of the observations and the results are discussed.     

Ultrastructure and formation of hooded hooks in Capitella capitata (Annelida, Capitellida)

 The hooded hooks of Capitella capitata are aligned in a transverse row inside each neuro- and notopodial rim of the last thoracic and all abdominal setigers. Each seta consists of a rostrum, a capitium, the spines of which surmount the rostrum, and a long, sigmoid shaft or manubrium, towards which rostrum and capitial spines are curved. A thin hood, complete except for a subapical opening and a short, subrostral cleft, encloses the apical portions of the seta. Generally, the tip of the rostrum extends beyond the hood. The hood consists of an outer and an inner lamella, between which is a compartment loosely filled with fibrillar material. Hooded hooks are generated at the dorsal edge of the neuropodial rim and at the ventral edge of the notopodial rim during the entire life of C. capitata. Chaetogenesis starts in a small compartment surrounded by the basal chaetoblast and four follicle cells. Initially a group of microvilli emanating from the chaetoblast preforms the rostrum. Next, stout microvilli appear adrostrally, each preforming a spine of the capitium. When both structures have been formed, the longitudinal axis of the anlage shifts, because the actin filaments inside the microvilli reorientate and initiate formation of the manubrium. During this initial phase of chaetogenesis the anlage sinks into the chaetoblast, until the latter finally enwraps the anlage, except the tip of the rostrum. The chaetoblast now generates microvilli that face the new setal structures and preform the hood. During further development the microvilli separate into two layers, an inner and an outer one. The inner layer of microvilli merges with the manubrium prior to the outer layer. Addition of setal material occurs between the bases of the microvilli and elongates the manubrium until it extends beyond the epidermal surface. The microvilli, which have continuously been withdrawn from the seta during chaetogenesis, remain in the basal section. Specific morphogenetic and structural correspondence between the hooked setae of species of Maldanomorpha, Psammodrilida and Oweniida, the uncini of species of the Sabellida, Terebellida and Pogonophora, and the hooded hooks of species of Capitellidae justify the hypothesis that all these setae are homologous. This hypothesis implies the existence of a monophyletic group consisting of all polychaetous Annelida with such setae. Accepted: 16 December 1997     

The structure of anoline (Reptilia: Dactyloidae: Anolis) toe pads in relation to substratum conformity

Adhesive toe pads of geckos house modified components of vascular and/or connective tissues that promote conformity of the setal fields with the locomotor substratum. Similar modifications have been claimed for the digits of Anolis, but evidence for them is not compelling. Angiographic and histological investigations of Anolis failed to identify any evidence of either an intralamellar vascular reticular network or a central sinus. Instead, their vascularity more closely resembles that of lizards in general than that of pad‐bearing geckos. The loose connective tissue of the toe pads likely contributes to their general pliability and flexibility, promoting localized compliance with the substratum. Through the shedding cycle, the lamellae change shape as the replacing setae elongate. The outer epidermal generation lacunar cells on the inner lamellar faces simultaneously hypertrophy, providing for compatibility between overlapping lamellae, enabling reciprocity between them. This contributes to continuing compliance of the setal fields with the substratum. Overall, digital structure and attachment and release kinematics of the toe pads of Anolis are very similar to those of geckos exhibiting an incipient adhesive mechanism. Both lack major anatomical specializations for promoting conformity of the setae with the locomotor substratum beyond those of the seta‐bearing portions of the epidermis.     

Histochemical and ultrastructural analyses of adhesive setae of lizards indicate that they contain lipids in addition to keratins

We studied the distribution of lipid material and organelles in the epidermal layers of toe pads from two species of lizards representing the two main lizard families in which adhesive scansors are found (gekkonids and polychrotids), the dull day gecko, Phelsuma dubia and the green anole, Anolis carolinensis. Although lipids are a conspicuous component of the mesos layer of squamate reptiles and function in reducing cutaneous water loss, their distribution has not been specifically studied in the highly elaborated epidermal surface of adhesive toe pads. We found that, in addition to the typical cutaneous water loss‐resistant mesos and alpha‐layer lipids, the Oberhäutchen (including the setae) on the most exterior layers of the epidermis in P. dubia and A. carolinensis also contain lipid material. We also present detailed histochemical and ultrastructural analyses of the toe pads of P. dubia, which indicate that lipid material is closely associated spatially with maturing setae as they branch during the renewal phase of epidermal regeneration. This lipid material appears associated with the packing of keratin within setae, possibly affecting permeability to water loss in the pad lamella, where the surface area is from 4–60‐fold greater compared with normal scales. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Setal Structure and Chaetogenesis in Scolelepis squamata and Malacoceros fuliginosus (Spionidae,Annelida)

In Scolelepis squamata and Malacoceros fuliginosus two alternatingly arranged transverse rows of setae are found in each ramus. These are capillary setae in all thoracic setigers, whereas in abdominal setigers they may alternate with hooded hooks. In M. fuliginosus only the abdominal neuropodia bear hooded hooks, whereas in S. squamata these setae are present in both rami in the abdomen. Here every second seta (the capillary one) degenerates before its formation is complete, leading to a single row of hooded hooks. In the transverse rows new setae are formed in a medio-lateral formative site in both species. Additionally in each ramus there exists one longitudinal row of capillaries which each possesses its own formative site. Ultrastructure and formation of the hooded hooks in S. squamata is very similar to that of hooded hooks in Capitellidae. The hood is preformed by a certain group of microvilli of the chaetoblast, which soon differentiates two layers of microvilli, raising an inner and an outer hood lamella. The hooded hooks and their arrangement are regarded as homologous characters in Spionidae and Capitellidae. This indicates a closer relationship of Spionidae with a taxon consisting of Capitellidae, Arenicolidae, Maldanidae, Oweniida, Terebellida, Sabellida, and Pogonophora.     

AN AUTORADIOGRAPHIC AND HISTOCHEMICAL LOCALIZATION OF SULFATED POLYSACCHARIDES IN EUCHEUMA NUDUM (RHODOPHYTA)1

The predominant sulfated polysaccharide, ?-carrageenan, was localized in the middle lamella of epidermal, cortical and medullary cells of Eucheumanudum J. Agardh. Autoradiographic studies with ³⁵SO₄= indicated that the label was first incorporated in the inner wall and ultimately deposited in the middle lamella of all cells, and in an outer wall layer of the epidermal cells. There was no evidence for cytoplasmic incorporation of the label. The middle lamella stained with alcian blue, was γ-metachromatic with toluidina blue O and bound diaminobenzidine-osmium tetroxide. This region was also positive with periodic acid-Schiff's (PAS) ragent, possibly demonstrating cellulose and/or a nonsulfated precursor of ?-carrageenan. A proposed model for extracellular sulfation includes production and secretion of a nonsulfated polygalactan and sulfotransferase enzyme(s) by the golgi apparatus and endoplasmic reticulum, respectively. Free sulfate in the wall would be bound to the precursor polysaccharide, with much of the resulting carrageenan migrating to the middle lamella facilitating mutual cell growth.     

Giselinidae fam. nov., a new monophyletic group of cyclopoid copepods (Copepoda, Crustacea) from the Atlantic deep sea

Four new species of Cyclopoida from deep-sea waters are described and placed in two new genera: Giselina gen. n. and Sensogiselina gen. n. The new genera and species belong to a new monophyletic group within the cyclopinid cyclopoids. A new name, Giselinidae, is proposed for this monophylum. The new family is characterised by the combination of the following characters: (1) tergite of leg 1 fused to cephalosome dorsally, but incompletely fused laterally, (2) absence of aesthetascs on ancestral antennulary segments XVI, XXI and XXV, (3) absence of antennary exopodal setae, (4) presence of only three spines on distal exopodal segment of leg 1, (5) absence of inner setae on first endopodal segments of legs 1–4, (6) outer terminal and distal inner elements of distal endopodal segment of leg 4 transformed into spines, (7) distal outer element of leg 5 exopod transformed into a spine, (8) leg 6 with only one seta, and (9) furcal setae I and III located on dorsal margin. Received in revised form: 16 June 2000 Electronic Publication     

Expression of the HB9 homeobox gene concomitant with proliferation accompanying epidermal stratification during development of chick embryonic tarsometatarsal skin

A homeobox gene, HB9, has been isolated from the tarsometatarsal skin of 13-day-old chick embryos using a degenerate RT-PCR-based screening method. In situ hybridization analysis revealed that, during development of chick embryonic skin, the HB9 gene was expressed in epidermal basal cells of the placodes, but not in those of interplacodes, and in the dermal cells under the placodes at 9 days before addition of an intermediate layer by proliferation of the basal cells in the placodes. With the onset of epidermal stratification, the direction of the basal cell mitosis changed, with the axis becoming vertical to the epidermal surface. Placodes and interplacodes form outer and inner scales, respectively, after they have elongated distally (Tanaka S, Kato Y (1983b) J Exp Zool 225: 271–283). During scale ridge elongation at 12–15 days, HB9 was strongly expressed in the epidermis of the outer scale face, where the cell proliferation is more active than in the epidermis of the inner scale face; hence, stratification of the outer scale face is more prominent than that of the inner scale face. After 16 days, when mitotic activity in the epidermal basal cells decreases and the thickness of the epidermis is maintained at a constant level, the HB9 expression decreases with the onset of epidermal keratinization. These results suggest that HB9 may be involved in the proliferation of the epidermal basal cells that accompanies epidermal stratification.     

A new species of Ilyocryptus (Anomopoda: Macrothricidae) from Argentina

I. elegans n.sp. from the Parana River, northeastern Argentina is proposed and its morphological features are compared with those of the apparently related I. agilis. Its outstanding characteristics are the long 2rd to 5th setae of ventral margin of the valves, the rudimentary nature of defensive setae, the low number of spines in the preanal lobe of postabdomen and the unequality of the length of the setae in the outer distal lobe of first trunk limbs.Finding of this new species suggests that I. agilis would be a complex of species and its records should be revised.     

Surface structures of the antennular flagella of the hermit crab Pagurus alaskensis (Benedict): A light and scanning electron microscopy study

The surface structures of the antennular flagella of Pagurus alaskensis are described in detail. Attention is directed towards the surface morphology of two types of possible sensilla: (1) exoskeletal pores (1.0–3.0 μm in diameter); (2) setae of various kinds. In addition, small (0.1–0.2 μm) pits occur in the exoskeleton which are not considered to be sensory in function. The exoskeletal pores are found at fairly specific locations on both the inner and outer flagella, particularly on the short segments of the outer flagella. Neither the inner nor the outer flagella are bilaterally symmetrical with respect to their setal armature. On the outer flagellum six groups of setae may be distinguished: lateralmesial; dorsal; ventral; accessory; aesthetasc; setae of the distal segment. On the inner flagellum setae of the mesial and lateral rows form distinctive groups. The morphology, orientation and locations of all the flagellar setae are defined and where possible the numbers of the various morphological types within the specific setal groups are given. It is noteworthy that many setal types have obvious apical pores and yet no pores could be found in the chemoreceptive aesthetasc setae. The functions of the various setae are discussed in relation to their topographical position and to existing electrophysiological and behavioral data. Some suggestions are made about future experiments to demonstrate the central connections of specific sensilla or groups of sensilla and to show their significance in the whole animal.     

Two new species of Diaphanosoma Fischer, 1850(Crustacea: Branchiopoda: Cladocera) from the United States

Two new species of the genus Diaphanosoma, D. oligosetum and D. dorotheae, from Louisiana and North Carolina respectively, are described. The former species has large head with protruding dorsal part, large lanceolate spine on the basipodite's distal outer end, an extremely reduced number of antennal setae, up to six in adult specimens, and unique armament of valve margin. On the whole, it shows the pronounced combination of primitive and specialized morphological traits. D. dorotheae is a member of D. brachyurum species group differing from its other known representatives in presence of a small but very conspicuous spine on the end of proximal segment of antennal exopodite and a variable number of setae (seven or eight) on the distal segment of the branch. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphogenesis of the digital pad lamellae in the embryo of the lizard Anolis lineatopus

The present study in the embryo of the lizard Anolis lineatopus describes the modality of cell proliferation responsible for the morphogenesis of the digital pad lamellae and of the epidermal stratification. After tritiated thymidine and 5-bromodeoxy-uridine administration, autoradiographic and immunocytochemical methods have been used. The lamellae originate as long, slightly slanted, undulations of the epidermis of fingers and toes. At an early stage, the epidermis consists of an outer periderm and a basal layer. Cell hypertrophy, and the prevalent cell proliferation in the longer side of the undulation with respect to the shorter side, generate the surface of the outer lamella. Under the peridermis, a shedding complex, composed by clear and oberhautchen layers, is formed and later determines the first intraepidermal shed. The first subperidermal layer derived from the basal layer is a clear layer and the first shed epidermis in the embryo is represented by periderm and clear layer. The heavily granulated clear layer in Anolis lineatopus represents the first epidermal layer produced in the embryonic epidermis, and is connected with the process of shedding. The spinulae of the underlying oberhautchen in the outer scale surface become long setae which grow toward the upper clear layer. Under the shedding complex a β-layer is produced. Autoradiographical study shows that the radioactivity stays in the basal layer for about 4 days before cells move to upper layers. At 6–8 days post-injection labelled cells are visible in the differentiated clear, oberhautchen and β-layers. Under the β-layer differentiating mesos cells are visible before the embryo hatches.     

A new species of the deep‐sea copepod genus Scutogerulus (Calanoida: Arietellidae) from the hyperbenthic waters of Okinawa,Japan

A new species of the rare arietellid genus Scutogerulus is described from deep hyperbenthic waters off Okinawa, southwestern Japan. This is the second species of the genus. Phylogenetically significant characteristics known only on the basis of the type species are confirmed by the discovery of the new congener, in particular: (1) the genital system of the female exhibits the most plesiomorphic condition of any arietellid genus; (2) the well developed setae on the endopodal segments of the maxillae and maxillipeds are modified into ‘shield‐like setae’ similar to the ‘button setae’ in another arietelloidean family, the Augaptilidae; (3) the outer distal spine on the first exopodal segment of leg 1 is absent.     

Distal invaginations and the renewal of cone outer segments in anuran and monkey retinas

Summary Although it is now clear that the outer segments of mature vertebrate cones are regularly renewed, it is not known how a cone outer segment can maintain a tapered shape if its narrower tip is periodically lost by shedding. This problem was addressed by morphological examination of photoreceptors in retinas of anurans (Xenopus laevis) and monkeys (Macaca fascicularis). Light microscopy revealed a marked daily change in the shape of cone outer segments in X. laevis: at light offset they were long and conical, at light onset they had shed their narrow tips, were sharply truncated, and 40% shorter. Electron microscopy revealed previously undescribed fine-structural features in these mature cone outer segments, most notably the presence of many partial membrane infoldings within their distal lamellae. The growth of each of these distal invaginations apparently split 1 pre-existing distal lamella into 2 daughter lamellae of reduced width. The formation of distal invaginations at various heights within a cone outer segment would thus make it longer and narrower. Similar ultrastructural features were also found in cone outer segments of monkey retinas. These findings suggest that during outer segment renewal the tapered shape of mature cone outer segments is maintained via a remodelling process that accompanies the formation of distal invaginations.Portions of this work have been published in abbreviated or preliminary form (Eckmiller 1988, 1989b, c)     

Ultrastructural Similarities Between Setae of Brachiopods and Polychaetes1

Larvae of the brachiopod Terebratalia transversa Sowerby have 2 bundles of setae on each side of their mantle lobe. Each seta grows out of a follicle of epidermal cells. The cisternae and associated vesicles of the Golgi bodies in lateral follicular cells are filled with electron dense material. The basal follicular cell, or chaetoblast, has apical microvilli projecting into the basal ends of the longitudinal channels of the seta. The channel partitions are composed of fine fibers oriented parallel to the setal axis. The close structural and developmental similarities between polychaete and brachiopod setae are discussed.     

The cellular pathway of sucrose transport in developing cotyledons ofVicia faba L. andPhaseolus vulgaris L.: a physiological assessment

The cellular pathway of sugar uptake in developing cotyledons of Vicia faba L. and Phaseolus vulgaris L. seed was evaluated using a physiological approach. The cotyledon interface with the seed coat is characterised by a specialised dermal cell complex. In the case of Vicia faba cotyledons, the epidermal component of the dermal cell complex is composed of transfer cells. Sucrose is the major sugar presented to the outer surface of both cotyledons and it is taken up from the apoplasm unaltered. Estimated sucrose concentrations within the apparent free space of Vicia and Phaseolus cotyledons were 105 and 113 mM respectively. Rates of in-vitro uptake of [¹⁴C]sucrose by cotyledon segments or by whole cotyledons following physical removal or porter inactivation of the outer cells demonstrated that, for both Vicia and Phaseolus cotyledons, the dermal cell complexes are the most intense sites of sucrose uptake. Accumulation of [¹⁴C]sucrose in the storage parenchyma of whole cotyledons was directly affected by experimental manipulation of uptake by the outer cell layers and plasmolytic disruption of the interconnecting plasmodesmata. These findings indicated that sucrose accumulated by the dermal cell complexes is transported symplasmically to the storage parenchyma. Overall, it is concluded that the dermal cell complexes of the developing legume embryo, irrespective of the presence or absence of wall ingrowths, are the major sites for the uptake of sucrose released from the maternal tissues to the seed apoplasm. Thereafter, the accumulated sucrose is transported radially inward through the symplast to the storage parenchyma.Abbreviations AFS apparent free space - CF 5-(6)-carboxyfluorescein - CFDA 5-(6)-carboxyfluorescein diacetate - Mes 2-(N-morpholino)ethanesulfonic acid - PCMBS p-chloromercuribenzenesulfonic acid - SRG sulphorhodamine G The investigation was supported by funds from the Research Management Committee, The University of Newcastle and the Australian Research Council. One of us, R. McDonald, gratefully acknowledges the support of an Australian Postgraduate Research Award. We are grateful to Stella Savoury for preparing the photomicrographs.