Histology of mental and caudal courtship glands in three genera of plethodontid salamanders (Amphibia: Plethodontidae)

Salamanders in the family Plethodontidae exhibit a unique tail‐straddle walk during courtship that can include the use of sexually dimorphic mental and caudal courtship glands. This study presents novel histological and fine structure data on mental glands and caudal courtship glands in Plethodon mississippi, Desmognathus conanti and Eurycea quadridigitata using both light microscopy and scanning electron microscopy. This study represents the first use of scanning electron microscopy to observe these glands. Both mental and caudal courtship glands were observed to vary seasonally in gland diameter and histology according to the breeding season of each species. Morphological variation was observed across the three species studied in both clustering and relative size of the glands compared to neighbouring mucous and granular glands. Hypertrophied mental glands are larger than mucous or granular glands in all species, but relationships among caudal courtship glands and other skin glands vary among species. In E. quadridigitata, active caudal courtship glands are larger than mucous and granular glands, but in D. conanti, caudal courtship glands are similar in size to granular glands and larger than mucous glands. In P. mississippi, caudal courtship glands are scattered among significantly larger granular glands and are similar in size to mucous glands.     

Innervation of skin glands in the frog

Summary A comparative study was undertaken on the innervation of mucous and granular glands in frog skin. Results obtained by the Falck-Hillarp fluorescence technique and cholinesterase staining indicated that both types of glands receive exclusively adrenergic innervation. Electron microscopy was used to investigate the innervation pattern at the ultrastructural level. The distribution of nerve terminals was found to differ in the two types of glands. In the mucous gland, terminals were found at a distance of about 0.5 m from the basement membrane but never within the gland parenchyma. In the granular gland, the terminals were located between smooth muscle cells and also in direct contact with the secretory epithelium but never outside the basement membrane.This work was carried out in part at King Gustaf V:s Forskningsinstitut, Stockholm, and was supported by a grant from Karolinska Institutet     

The architecture of the accessory reproductive glands of the male desert locust: 1: types of glands and their secretions

The accessory reproductive glands of the male desert locust were studied by histological, histochemical, and phase-contrast techniques. It was found that the characteristics of the glandular epithelium and their corresponding secretions permit the division of the accessory glands into nine distinct types. Three types produce coarsely granular mucopolysaccharide secretions (glands 1, 11, and 12); three types produce finely fibrous mucopolysaccharide secretions (glands 2, 4, and 7-10, 13-15); one type produces a globular mucopolysaccharide or mucoproteinaceous secretion (gland 6); one type produces an acidic lipoprotein complex (glands 3 and 5); and one is the functional seminal vesicle (gland 16). Consequently, the various secretions are separated as a result of a vertical segregatign of the various cell types that are responsible for glandular activity.     

Loss of traditional mucous glands and presence of a novel mucus-producing granular gland in the plethodontid salamander Ensatina eschscholtzii

All amphibians are thought to possess two distinct types of dermal gland: mucous and granular. Mucous glands typically produce an acidic, flocculent and carbohydrate positive secretion that keeps skin moist and helps maintain homeostasis. In this study, we use a battery of histochemical tests to identify these traditional mucous glands in the dermis of the plethodontid salamander Ensatina eschscholtzii . The periodic acid-Schiff, alcian blue, toluidine blue and carmine reactions reveal the absence of both acidic glycosaminoglycans and traditional mucous glands. Instead, E. eschscholtzii produces neutral mucus in specialized granular glands, which we name mucus-producing granular glands (MPGGs). The loss of traditional mucous glands is a derived trait for Ensatina .  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 469–477.     

An insight into the skin glands,dermal scales and secretions of the caecilian amphibian Ichthyophis beddomei

The caecilian amphibians are richly endowed with cutaneous glands, which produce secretory materials that facilitate survival in the hostile subterranean environment. Although India has a fairly abundant distribution of caecilians, there are only very few studies on their skin and secretion. In this background, the skin of Ichthyophis beddomei from the Western Ghats of Kerala, India, was subjected to light and electron microscopic analyses. There are two types of dermal glands, mucous and granular. The mucous gland has a lumen, which is packed with a mucous. The mucous-producing cells are located around the lumen. In the granular gland, a lumen is absent; the bloated secretory cells, filling the gland, are densely packed with granules of different sizes which are elegantly revealed in TEM. There is a lining of myo-epithelial cells in the peripheral regions of the glands. Small flat disk-like dermal scales, dense with squamulae, are embedded in pockets in the dermis, distributed among the cutaneous glands. 1–4 scales of various sizes are present in each scale pocket. Scanning electron microscopic observation of the skin surface revealed numerous glandular openings. The skin gland secretions, exuded through the pores, contain fatty acids, alcohols, steroid, hydrocarbons, terpene, aldehyde and a few unknown compounds.     

Ultrastructure and histochemistry of the foregut in<Emphasis Type="Italic"> Wirenia argentea</Emphasis> and<Emphasis Type="Italic"> Genitoconia rosea</Emphasis> (Mollusca,Solenogastres)

Wirenia argentea and Genitoconia rosea feed on Cnidaria like most representatives of the molluscan taxon Solenogastres (Aplacophora, Neomeniomorpha sensu Scheltema). The structure and histochemistry of the foregut are described based on histologic, semithin, and ultrathin section series. The ultrastructure was analyzed by means of transmission electron microscopy. There are two sets of unicellular glands: a narrow row of preoral gland cells opening to the preoral area, and pharyngeal gland cells in high numbers. Preoral gland cells produce serous secretions in W. argentea, but mucosubstances in G. rosea, whereas pharyngeal gland cells are similar in structure and histochemistry in both species. Based on the size and electron density of gland vesicles, five distinct types of pharyngeal gland cells can be defined. In contrast to earlier assumptions, all types of pharyngeal gland cells produce serous secretions, most probably representing digestive ferments, but no mucosubstances.     

Structure of male accessory glands of Bolivarius siculus (fischer) (Orthoptera,Tettigoniidae) and protein analysis of their secretions

In Tettigoniidae (Orthoptera), male reproductive accessory glands are involved in the construction of a two‐part spermatophore; one part, the spermatophylax, is devoid of sperm and considered a nuptial gift. The morphology, ultrastructure, and secretion protein content of the male reproductive accessory glands from Bolivarius siculus were investigated. Two main groups of gland tubules open into the ejaculatory duct: the “first‐order” glands, a number of large anterior tubules, and the “second‐order” glands, smaller and more numerous tubules positioned posteriorly. Along with a further subdivision of the gland tubules, we here describe for the first time an additional gland group, the intermediate tubules, which open between first and second‐order glands. The mesoderm‐derived epithelium of all glands is a single layer of microvillated cells, which can be either flattened or cylindric in the proximal or distal region of the same gland. Epithelial cells, very rich in RER and Golgi systems, produce secretions of both electron‐dense granules and globules or electron‐transparent material, discharged into the gland lumen by apocrine or merocrine mechanisms, respectively. With one exception, a unique electrophoresis protein profile was displayed by each of the gland types, paralleling their unique morphologies. To assess the contribution of different types of accessory glands to the construction of the spermatophore, the protein patterns of the gland secretions were compared with those of the extracts from the two parts of the spermatophore. All samples showed bands distributed in a wide range of molecular weight, including proteins of very low molecular mass. However, one major high molecular weight protein band (>180 kDa) is seen exclusively in extracts from the first‐order glands, and corresponds to an important protein component of the spermatophylax. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Ultrastructure of esophageal glands and their secretory granules in the root-knot nematodeMeloidogyne incognita

Summary The dorsal and subventral esophageal glands and their secretory granules in the root-knot nematodeMeloidogyne incognita changed during parasitism of plants. The subventral esophageal glands shrank and the dorsal gland enlarged with the onset of parasitism. While secretory granules formed by both types of glands were spherical, membrane-bound, and Golgi derived, the granules differed in morphology and size between the two types of glands. Subventral gland extensions in preparasitic second-stage juveniles were packed with secretory granules which varied in diameter from 700–1,100 nm and had a finely granular matrix. Within the matrix of each subventral gland granule was an electron-transparent core that contained minute spherical vesicles. The size and position of the core varied within different granules. Few granules were present in the dorsal gland extension in preparasitic juveniles. The matrix of dorsal gland secretory granules formed during parasitism was homogeneous and more electron-dense than the matrix of subventral gland granules. Subventral gland secretory granules of parasitic juveniles and adult females appeared degenerate.     

Fine structure of axons associated with the salivary apparatus of the cockroach, Nauphoeta cinerea

Previous studies have shown that the neurotransmitter at the salivary gland of the cockroach is probably dopamine. An ultrastructural study of the innervation of these glands was made. It was concluded that there are two types of axon present designated type A and type B. Type A axons possess small agranular elliptical vesicles and large granular vesicles, whereas type B possess only large granular vesicles of larger diameter than those found in type A. The relationship of these types of axon to the cells of the acini is discussed. It is concluded that type A axons are catecholaminergic.     

Hopping locomotion in a nematode: Functional anatomy of the caudal gland apparatus of Theristus caudasaliens sp. n.

The interstitial nematode Theristus caudasaliens n. sp. normally locomotes by hopping on the left side of its tail tip, a mode of locomotion that is unique among nematodes. The animal uses its caudal glands and caudal musculature to perform the hops, attaching itself momentarily between hops with the glands and executing the hops by straightening and curling the posterior part of its body. The caudal gland apparatus can be seen by electron microscopy to consist of five gland cells of two different types. Three of these cells, termed viscid glands, are involved in adhesion of the animal to substrates and produce ovoid granules with a central dense band. The other two cells are characterized by smaller, lessdense granules and presumably function in releasing the animal from substrates. The ducts of both gland types extend to the tail tip where they terminate in a common crescent-shaped space. Their secretions are released to the outside through two pores on the left side of the tail tip. There is no spinneret valve in this nematode. The muscles of the tail and of the mid-body region are developed to the same extent. The caudal gland apparatus can be compared with the duo-gland adhesive organs of other interstitial animals, but its homology with either these organs or the caudal glands of other nematodes is uncertain. Theristus caudasaliens is described as a new species.     

Anatomy and ultrastructure of the female reproductive system of Pleioplana atomata (Platyhelminthes: Polycladida)

The ultrastructure of the female reproductive system of the polyclad flatworm Pleioplana atomata is described. Numerous ovaries are scattered throughout the entire body but are mainly concentrated on the dorsal side. Within an ovary, a germinative zone with oogonia and prefolicular cells is located in the dorsal part of the ovary. The remaining part of the gonad is filled with previtellogenic and early vitellogenic oocytes enwrapped by follicular cells. During previtellogenesis, oocytes produce numerous eggshell globules, which are distributed into the cortical area of the cell in later stages. Eventually, these globules release their contents into the space between the eggshell cover and oolemma. Similar types of globules are also found in others flatworms, and may represent useful phylogenetic characters. Entolecital, vitellogenic oocytes pass to paired uteri, where vitellogenesis is completed. The remainder of the female reproductive system consists of paired thin uterine ducts that join a vagina. The distal part of the long, curved vagina forms a large Lang's vesicle, while the proximal part is connected to a female atrium leading to a female gonopore. We hypothesize that Lang's vesicle functions in the digestion of excess sperm received. Two kinds of different shell (cement) glands that release their secretion into the vagina are identified. Both are unicellular glands and each gland cell connects to the lumen of the vagina via an individual canal. Similar glands in other acotylean polyclads have been implicated in the formation of eggshell covers. J. Morphol. 2009. © 2008 Wiley‐Liss, Inc.     

Ultrastructure of multicellular foregut glands in selected Solenogastres (Mollusca)

Foregut glands in Solenogastres are not only of importance in biological processes like feeding and digestion, but multicellular foregut glands also provide valuable characters for taxonomy and systematics. Here, the fine structure of four different types of foregut glands is investigated: the Meioherpia-type ventrolateral foregut gland of Meioherpia atlantica, the Simrothiella-type ventrolateral foregut gland of Simrothiella cf. margaritacea, and the Pararrhopalia-type ventrolateral foregut gland as well as the dorsal gland of Pararrhopalia pruvoti. Thereby, special focus is set on the arrangement of glandular and supporting cells within the glands, and on the characterization of glandular cells according to the size, shape and electron-density of their secretional vesicles. It is shown that the investigated glands are complex organs composed of non-glandular supporting cells and two to five glandular cell types producing discrete secretions.     

Granular cutaneous glands in the frog Physalaemus biligonigerus (Anura, Leptodactylidae): comparison between ordinary serous and 'inguinal' glands

Beside the ordinary granular (or serous) glands, the skin of the leptodactylid frog Physalaemus biligonigerus possesses peculiar clusters of large granular units, the 'inguinal' glands, located in the dorsolateral areas of the pelvic girdle. Both gland types store their specific products within the syncytial cytoplasm of the secretory unit. These secretory materials consist of spheroidal or ellipsoidal bodies (granules) with a repeating substructure. The subcellular features of the immature products of the ordinary serous and inguinal glands are identical. However, these products undergo divergent maturative processes, leading to fluidation on the one hand and condensation on the other. Secretory release into the small gland lumen was observed in both cases, involving merocrine mechanisms. On the basis of the analysis of cutaneous serous gland polymorphism in anurans, the inguinal units in P. biligonigerus do not appear to be an independent line. Rather, these large units belong to the ordinary serous type and represent a gland population specialized in the storage of remarkable amounts of product used in chemical defence of the skin.     

Receptors for the neuropeptides,myoinhibitory peptide and SIFamide,in control of the salivary glands of the blacklegged tick Ixodes scapularis

Tick salivary glands are important organs that enable the hematophagous feeding of the tick. We previously described the innervation of the salivary gland acini types II and III by a pair of protocerebral salivary gland neurons that produce both myoinhibitory peptide (MIP) and SIFamide (?imo et al., 2009b). In this study we identified authentic receptors expressed in the salivary glands for these neuropeptides. Homology-based searches for these receptors in the Ixodes scapularis genome sequence were followed by gene cloning and functional expression of the receptors. Both receptors were activated by low nanomolar concentrations of their respective ligands. The temporal expression patterns of the two ligands and their respective receptors suggest that the SIFamide signaling system pre-exists in unfed salivary glands, while the MIP system is activated upon initiation of feeding. Immunoreactivity for the SIFamide receptor in the salivary gland was detected in acini types II and III, surrounding the acinar valve and extending to the basal region of the acinar lumen. The location of the SIFamide receptor in the salivary glands suggests three potential target cell types and their probable functions: myoepithelial cell that may function in the contraction of the acini and/or the control of the valve; large, basally located dopaminergic granular cells for regulation of paracrine dopamine; and neck cells that may be involved in the control of the acinar duct and its valve.     

Ultrastructural and histochemical study of the salivary glands of Aplysia depilans (Mollusca, Opisthobranchia)

The digestive system of the sea hare, Aplysia depilans , includes a pair of ribbon-shaped salivary glands. A central duct and a large blood vessel run close to each other along the length of these glands and both are surrounded by a layer of muscle cells. Three cell types form the glandular epithelium: granular cells, vacuolated cells and mucocytes. The granular cells possess cilia and spherical secretion granules, located primarily in the apical region. The granules of immature cells have a low electron density and are mainly formed by neutral polysaccharides with small amounts of proteins. The granules of mature cells are larger, have a high electron density and are mainly formed by proteins with lower amounts of neutral polysaccharides. Transition stages between immature and mature granular cells are observed. The vacuolated cells are large and frequently pyramidal in shape, but after the application of histochemical techniques almost all vacuoles remain uncoloured. The numerous vacuoles contain flocculent material in a clear background and the mitochondria possess large crystalline structures in the matrix. A pyramidal shape is also typical of the mucocytes, which are filled with vesicles containing granular masses surrounded by a network of secretion material. These large cells are strongly stained by Alcian blue, revealing the presence of acidic mucopolysaccharides. This is the first ultrastructural study of the salivary glands in opisthobranch gastropods.     

The dorsal tail tubercle of Mertensiella caucasica and M. luschani (Amphibia: Salamandridae)

Males of the two species of Mertensiella (M. caucasica and M. luschani) possess a tubercle projecting from the skin of the dorsal tail base, the single morphological character that defines the genus. The dorsal tail tubercle functions during courtship, and its role is similar in both species. The tubercle is inserted into the cloaca of the female during ventral amplexus, shortly before the male deposits a spermatophore. Histological examination, however, revealed that the dorsal tubercles differ structurally between the two species. In M. caucasica, the tubercle consists primarily of elongate mucous glands, with granular glands occurring only at the base. Both mucous and granular glands of the tubercle are larger than those in typical skin. Unlike typical skin, however, mucous glands are larger than granular glands. In M. luschani, mucous glands and granular glands occur throughout the tubercle, and the granular glands are larger than the mucous glands, although both types are larger than those in typical skin. The dorsal tubercles of M. caucasica and M. luschani may not be homologous structures and may have resulted from convergent evolution. J Morphol 232:93–105, 1997. © 1997 Wiley-Liss, Inc.     

Morphology of the salivary glands of three Squamata species: Podarcis sicula sicula, Tarentola mauritanica and Coluber viridiflavus

The histology, histochemistry and ultrastructure of the salivary glands of three species of squamata, Podarcis sicula sicula (mandibular glands), Tarentola mauritanica (sublingual gland) and Coluber viridiflavus (supra- and infralabial glands) were studied. Each gland contained acidic cells, positive for both periodic acid Schiff and Alcian blue reactions. These cells can be distinguished as seromucous and mucous types based on the different electron density of their granules. α-Amylase, until now detected only in mammalian salivary glands, was not found in any of the salivary glands examined. The ultrastructural study revealed that the salivary glandular cells of T. mauritanica lack intercellular canaliculi, which by contrast, are present between the seromucous cells in the salivary glands of C. viridiflavus and P. s. sicula . Comparable variation is also seen when the ultrastructural features of the secretory granules in salivary glands of the three Squamata species are compared. The salivary granules of T. mauritanica and C. viridiflavus are more or less dense but structureless, while the mucous granules of P. s. sicula have a distinctive and characteristic substructure. Therefore, this study, designed to obtain comparative data on the histology, histochemistry and ultrastructure of the salivary glands of three representative, but hitherto unstudied, species of Squamata, reveals great variation in the structure of these glands within the Squamata lineage, even when compared to previously documented species.     

Ultrastructural investigation of a salivary gland in a centipede: structure and origin of the maxilla I-gland of Scutigera coleoptrata (Chilopoda, Notostigmophora)

The maxilla I-gland of Scutigera coleoptrata was investigated using light and electron microscopy methods. This is the first ultrastructural investigation of a salivary gland in Chilopoda. The paired gland opens via the hypopharynx into the foregut and extends up to the third trunk segment. The gland is of irregular shape and consists of numerous acini consisting of several gland units. The secretion is released into an arborescent duct system. Each acinus consists of multiple of glandular units. The units are composed of three cell types: secretory cells, a single intermediary cell, and canal cells. The pear-shaped secretory cell is invaginated distally, forming an extracellular reservoir lined with microvilli, into which the secretion is released. The intermediary cell forms a conducting canal and connects the secretory cell with the canal cell. Proximally, the intermediary cell bears microvilli, whereas the distal part is covered with a distinct cuticle. The cuticle is a continuation of the cuticle of the canal cells. This investigation shows that the structure of the glandular units of the salivary maxilla I-gland is comparable to that of the glandular units of epidermal glands. Thus, it is likely that in Chilopoda salivary glands and epidermal glands share the same ground pattern. It is likely that in compound acinar glands a multiplication of secretory and duct cells has taken place, whereas the number of intermediary cells remains constant. The increase in the number of salivary acini leads to a shifting of the secretory elements away from the epidermis, deep into the head. Comparative investigations of the different head glands provide important characters for the reconstruction of myriapod phylogeny and the relationships of Myriapoda and Hexapoda.     

Serous gland dimorphism in the skin of Melanophryniscus stelzneri (Anura: Bufonidae)

Two serous gland types (I and II) in the skin of the Argentine toad Melanophryniscus stelzneri were discovered using light and electron microscopy. Glands of the two types differ in several traits: features of the products (both mature and immature), organelles involved in biosynthesis, and paths of serous maturation. No consistent differences, however, were detected between the myoepithelial sheaths encircling the secretory units. Type I glands manufacture vesicles containing a single dense body with a repeating substructure and conform to the fundamental secretory line of bufonid skin, a secretory line involved in biosynthesis of steroids. Type II glands synthesize granules of varying densities and seem to belong to a line of glands that secrete proteinaceous products. The occurrence of the two serous gland types in Melanophryniscus stelzneri is discussed in a comparison with current literature on the morphofunctional characteristics of anuran poison glands, which perform both regulative and defensive roles. It is suggested that di- or polymorphism in serous glands is an adaptive trait that allows differential release of active molecules on the body surface. J. Morphol. 237:19–32, 1998. © 1998 Wiley-Liss, Inc.