Ultrastructural features of the salt gland of Tamarix aphylla L.

Summary The salt gland in Tamarix is a complex of eight cells composed of two inner, vacuolate, collecting cells and six outer, densely cytoplasmic, secretory cells. The secretory cells are completely enclosed by a cuticular layer except along part of the walls between the collecting cells and the inner secretory cell. This non-cuticularized wall region is termed the transfusion are (Ruhland, 1915) and numerous plasmodesmata connect the inner secretory cells with the collecting cells in this area. Plasmodesmata also connect the collecting cells with the adjacent mesophyll cells.There are numerous mitochondria in the secretory cells and in different glands they show wide variation in form. In some glands wall protuberances extend into the secretory cells forming a labyrinth-like structure; however, in other glands the protuberances are not extensively developed. Numerous small vacuoles are found in some glands and these generally are distributed around the periphery of the secretory cells in association with the wall protuberances. Further, an unusual structure or interfacial apparatus is located along the anticlinal walls of the inner secretory cells. The general structure of the gland including the cuticular encasement, connecting plasmodesmata, interfacial apparatus, and variations in mitochondria, vacuoles, and wall structures are discussed in relation to general glandular function.     

Differences in protodermal cell wall structure in zygotic and somatic embryos of <Emphasis Type="Italic">Daucus carota</Emphasis> (L.) cultured on solid and in liquid media

The ultrastructure, cuticle, and distribution of pectic epitopes in outer periclinal walls of protodermal cells of Daucus carota zygotic and somatic embryos from solid and suspension culture were investigated. Lipid substances were present as a continuous layer in zygotic and somatic embryos cultured on solid medium. Somatic embryos from suspension cultures were devoid of cuticle. The ultrastructure of the outer walls of protodermis of embryos was similar in zygotic and somatic embryos from solid culture. Fibrillar material was observed on the surface of somatic embryos. In zygotic embryos, in cotyledons and root pectic epitopes recognised by the antibody JIM5 were observed in all cell walls. In hypocotyls of these embryos, these pectic epitopes were not present in the outer periclinal and anticlinal walls of the protodermis. In somatic embryos from solid media, distribution of pectic epitopes recognised by JIM5 was similar to that described for their zygotic counterparts. In somatic embryos from suspension culture, pectic epitopes recognised by JIM5 were detected in all cell walls. In the cotyledons and hypocotyls, a punctate signal was observed on the outside of the protodermis. Pectic epitopes recognised by JIM7 were present in all cell walls independent of embryo organs. In zygotic embryos, this signal was punctate; in somatic embryos from both cultures, this signal was uniformly distributed. In embryos from suspension cultures, a punctate signal was detected outside the surface of cotyledon and hypocotyl. These data are discussed in light of current models for embryogenesis and the influence of culture conditions on cell wall structure.     

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.     

Developmental Ultrastructure of Glandular Trichomes of <Emphasis Type="Italic">Rosmarinus officinalis</Emphasis>: Secretory Cavity and Secretory Vesicle Formation

Glandular trichomes in the leaf lamina of Rosmarinus officinalis L. were examined by scanning and transmission electron microscopy. The leaves were characterized by an abundance of two types of glandular trichomes—small capitate and large peltate glandular trichomes. In addition to the glandular trichomes, numerous non-glandular trichomes were present on the abaxial surface of the leaf. These trichomes mainly predominated on the midrib, whereas glandular trichomes occurred on non-vein areas. At the initial phase of secretory cavity formation, hyaline areas were abundant in periclinal walls of head cells, while they were not observed in the anticlinal walls. The hyaline areas gradually increased in size, fusing with other areas throughout the wall. Loose wall material adjacent to hyaline areas was released from the head cell walls and migrated into the secretory cavities. As the secretory cavities continued to enlarge, the new vesicles emerging into the secretory cavities from the walls of head cells became surrounded with the surface of a typical membrane. They developed a round shape, but the contours of the vesicle surfaces appeared polygonal when tightly packed inside a cavity. These vesicles varied in size; small vesicles often possessed electron-dense contents, while large vesicles contained electron-light contents.     

Structure and ultrastructure of leaf and calyx glands in Galphimia brasiliensis (Malpighiaceae)

The present study describes the anatomical structure of calyx and leaf glands in Galphimia brasiliensis and analyzes the mechanism of secretion. The glands are marginal and suprabasal, cup-shaped, sessile, and scarcely visible with the naked eye. Light microscopy reveals the following features: a thin, smooth cuticle; unistratified secretory cells; subglandular parenchyma; and vascular bundle supply composed of phloem and xylem with abundant druses of calcium oxalate. Transmission electron microscopy reveals the presence of secretory cells with conspicuous nuclei, dense cytoplasm, lipid droplets, numerous vesicles, mitochondria, Golgi, rough endoplasmic reticulum (RER), and elongated plastids with osmiophilic contents. The secretion reaches the apoplastic space and accumulates beneath the cuticle. Finally, the viscous, translucent exudate is eliminated by mechanical rupture of the cuticle. Histochemical analysis confirms that lipids are the main constituent. Small amounts of polysaccharides were also identified.     

Ultrastructure of epidermal glands in neotenic reproductives of the termite Prorhinotermes simplex (Isoptera: Rhinotermitidae)

The ultrastructure of epidermal glands in neotenic reproductives of Prorhinotermes simplex is described and their development is compared among young and old neotenics of both sexes. Secretory cells forming the epidermal gland are attached to the cuticle all over the body. The glands are formed by class 1 and class 3 secretory cells and corresponding canal cells with secretory function. Class 1 cells are sandglass-like and class 3 secretory units are located among them. Class 1 cells contain predominantly tubular endoplasmic reticulum, the major part represents the smooth and the minor the rough form. Numerous electron dense granules occur in the cytoplasm, they are always disintegrated prior to be released. Class 3 secretory cells contain a large amount of vacuoles, which are always lucent in males while newly produced vacuoles are dense in females. Dense vacuoles are frequently transformed into lucent ones before being released. Canal cells are locally equipped with microvilli. The conducting canal is surrounded by an electron dense secretion of regular inner structure. The cytoplasm of the canal cell contains numerous mitochondria, rough endoplasmic reticulum and a large proportion of microtubules. The young neotenic reproductives differ from the old ones by a lower amount of secretory products. Epidermal glands probably produce substances inhibiting the occurrence of superfluous reproductives.     

Organization of unusual idiosomal glands in a water mite, <Emphasis Type="Italic">Teutonia cometes</Emphasis> (Teutoniidae)

The unusual idiosomal glands of a water mite Teutonia cometes (Koch 1837) were examined by means of transmission and scanning electron microscopy as well as on semi-thin sections. One pair of these glands is situated ventrally in the body cavity of the idiosoma. They run posteriorly from the terminal opening (distal end) on epimeres IV and gradually dilate to their proximal blind end. The terminal opening of each gland is armed with the two fine hair-like mechanoreceptive sensilla (‘pre-anal external’ setae). The proximal part of the glands is formed of columnar secretory epithelium with a voluminous central lumen containing a large single ‘globule’ of electron-dense secretory material. The secretory gland cells contain large nuclei and intensively developed rough endoplasmic reticulum. Secretory granules of Golgi origin are scattered throughout the cell volume in small groups and are discharged from the cells into the lumen between the scarce apical microvilli. The distal part of the glands is formed of another cell type that is not secretory. These cells are composed of narrow strips of the cytoplasm leaving the large intracellular vacuoles. A short excretory cuticular duct formed by special excretory duct cells connects the glands with the external medium. At the base of the terminal opening a cuticular funnel strengthens the gland termination. At the apex of this funnel a valve prevents back-flow of the extruded secretion. These glands, as other dermal glands of water mites, are thought to play a protective role and react to external stimuli with the help of the hair-like sensilla.     

Ultrastructural changes in the pars distalis of the maturing male rat

Anterior pituitary glands of male rats (2, 3, 5, 8, 12, 25, 36, 52, 56, and 62 days of age) were processed for electron microscopy. During early postnatal stages secretory cells are found in various stages of differentiation and comparatively few secretory granules are seen. Nuclei are mostly irregular, and the nucleo-cytoplasmic ratio is large. Many free ribosomes are present; the endoplasmic reticulum is generally sparse and the Golgi complex small or invisible. Cells are of variable shape, and numerous cytoplasmic processes project into large intercellular spaces. Many electron-dense cells which often contain myelinlike figures are seen. Lysosomes and lysosomal precursors are frequently found in secretory cells, predominantly in somatotrophs, of all immature glands. Mitotic figures are numerous in early stages after brith and decrease in number as the gland grows in size. A gradual increase in cytoplasmic volume with concomitant differentiation of cytoplasmic components as well as accumulation of secretory granules, accompanied by loss of myelin-like figures and decrease in the number of electron-dense cells, is observed as the animal reaches the prepuberal stage. Few lysosomes are seen in cells of mature glands. At 36 days of age all secretory cells seem to have differentiated, and morphological features as well as granule content show little change until puberty is reached. Gonadotrophs attain their characteristic morphology later than other cells. Cilia are observed in all developmental stages but are relatively infrequent in the mature gland. The described ultrastructural characteristics reflect the degree of maturation as well as the functional capacities of secretory cells at particular stages of development.     

Ultrastructure of the male accessory glands ofAllacma fusca(Insecta, Collembola)

The accessory glands ofAllacma fusca(L.) (Insecta, Collembola, Sminthuridae) consist of a series of secretory units that are arranged in parallel and open into the ejaculatory duct. Each unit is composed of microvillate cells stacked around a common cavity. Basal cells are involved in ion-control of fluids from the hemocoel to the cavity. The intermediate and apical cells, which have a laminar appearance and contain many microtubules, are involved in the structural integrity of the unit. Supporting cells ensheath the most apical cells. Large openings in the cuticle allow the gland secretion to flow into the ejaculatory duct lumen. These openings are protected by a porous cuticle different from that lining the epithelium of the ejaculatory duct. Conspicuous muscle fibers run along the lateroventral side of the ejaculatory duct beneath the insertion of the accessory glands. The fine structure of the accessory glands indicates that they are type I ectodermic glands as defined by Noirot & Quennedey (1974). Their function could be to control the fluidity of the material for spermatophore formation and to ensure the proper physiological conditions for spermatozoa stored in the ejaculatory duct lumen.     

Fine structural aspects of secretory processes in a pentastomid arthropod parasite in its mouse and rattlesnake hosts

The histology and development of three extensive glands in the porocephalid pentastomid Porocephalus crotali is described by light and electron microscopy, during growth of the parasite to an infective stage in the tissues of mouse; the infective stage in rattlesnake definitive hosts is also included. These glands elaborate excretory/secretory components which are channelled, via chitin-lined efferent ductules, on to the parasite cuticle. Hook and frontal glands are relatively compact, and within each gland ductules serving individual secretory lobules collect into common ducts which discharge over each of the four hooks, or at the anterior margin of the cephalothorax respectively. Subparietal gland cell lobules, composed of two large and two small secretory cells, are distributed under the cuticle and each is served by a single efferent ductule; these erupt over the entire cuticle. The large cells in subparietal glands secrete lamellate droplets which coat the cuticle with thin layers. Identical cells are found in hook and frontal glands, in addition to to three morphologically distinct types of protein secretory cell. Preliminary data on the composition and immunological properties of the various secretory products are presented.     

Immunochemical localization of tetrahydrocannabinol (THC) in cryofixed glandular trichomes of Cannabis (Cannabaceae)

Delta 9-tetrahydrocannabinol (THC) localization in glandular trichomes and bracteal tissues of Cannabis, prepared by high pressure cryofixation-cryosubstitution, was examined with a monoclonal antibody-colloidal gold probe by electron microscopy (EM). The antibody detected THC in the outer wall of disc cells during the presecretory cavity phase of gland development. Upon formation of the secretory cavity, the immunolabel detected THC in the disc cell wall facing the cavity as well as the subcuticular wall and cuticle throughout development of the secretory cavity. THC was detected in the fibrillar matrix associated with the disc cell and with this matrix in the secretory cavity. The antibody identified THC on the surface of secretory vesicles, but not in the secretory vesicles. Gold label also was localized in the anticlinal walls between adjacent disc cells and in the wall of dermal and mesophyll cells of the bract. Grains were absent or detected only occasionally in the cytoplasm of disc or other cells of the bract. No THC was detected in controls. These results indicate THC to be a natural product secreted particularly from disc cells and accumulated in the cell wall, the fibrillar matrix and surface feature of vesicles in the secretory cavity, the subcuticular wall, and the cuticle of glandular trichomes. THC, among other chemicals, accumulated in the cuticle may serve as a plant recognition signal to other organisms in the environment.     

Study on pathway and characteristics of ion secretion of salt glands of Limonium bicolor

Recretohalophytes with specialized salt-secreting structures, including salt glands and salt bladders, can secrete excess salts from plant tissues and enhance salinity tolerance of plants. However, the pathway and property of salt secretion by the salt gland has not been elucidated. In the article, Limonium bicolor Kuntze was used to investigate the pathway and characteristics of salt secretion of salt gland. Scanning electron microscope micrographs showed that each of the secretory cells had a pore in the center of the cuticle, and the rice grain-like secretions were observed above the pore. The chemical composition of secretions from secretory pores was mainly NaCl using environmental scanning electron microscope technique. Non-invasive micro-test technology was used to directly measure ion secretion rate of salt gland, and secretion rates of Na⁺ and Cl^? were greatly enhanced by a 200-mmol/L NaCl treatment. However, epidermal cells and stoma showed little secretion of ions. In conclusion, our results provide evidence that the salt glands of L. bicolor have four secretory pores and that NaCl is secreted through these pores of salt gland.     

Venom gland ontogeny in Formicinae, with special reference to the pulvinate convoluted gland (Hymenoptera, Formicidae)

 The primordia of the sclerites associated with the venom gland appear in third-stage larvae. The study aims to link the structure and function of this specialised venom structure in Formicinae, together with glandular ontogeny, and puts emphasis on the relevance of the distinguished glandular subunits contributing to the final secretion. The most conspicuous changes in glandular development occur in the pharate pupa. At this stage, all subunits of the venom gland (the tubule, the convoluted gland and reservoir) are visibly present. Formation of the glandular cuticle starts around day 4 of the pupal stage. Luminal cells in the convoluted gland are provided with abundant free ribosomes and apical microvilli that remain during adult life. Stacks of granular endoplasmic reticulum are also frequently found in these cells. The convoluted gland contains relatively few scattered secretory cells, belonging to type 3 according to Noirot and Quennedey (1974), which contain electron-dense material in their extracellular spaces during adult life. These cells strongly contrast with the apparently general non-glandular nature of the convoluted gland tubule. Histochemical investigation of the secretory cells in the pulvinate convoluted gland reveals that these cells contain lipoid material, most likely to correspond with lipoids demonstrated in earlier chemical analyses. This lipoidal material in minor quantities strongly contrasts with the bulk of acid constituting the secretion. The substances produced in the convoluted gland could act as insulators, thus protecting the insect against its corrosive venom. Accepted: 28 April 1998     

Ultrastructure of the male reproductive accessory glands in the medfly Ceratitis capitata (Diptera: Tephritidae) and preliminary characterization of their secretions

The morphology and the ultrastructure of the male accessory glands and ejaculatory duct of Ceratitis capitata were investigated. There are two types of glands in the reproductive apparatus. The first is a pair of long, mesoderm-derived tubules with binucleate, microvillate secretory cells, which contain smooth endoplasmic reticulum and, in the sexually mature males, enlarged polymorphic mitochondria. The narrow lumen of the gland is filled with dense or sometimes granulated secretion, containing lipids. The second type consists of short ectoderm-derived glands, finger-like or claviform shaped. Despite the different shape of these glands, after a cycle of maturation, their epithelial cells share a large subcuticular cavity filled with electron-transparent secretion. The ejaculatory duct, lined by cuticle, has epithelial cells with a limited involvement in secretory activity. Electrophoretic analysis of accessory gland secretion reveals different protein profiles for long tubular and short glands with bands of 16 and 10 kDa in both types of glands. We demonstrate that a large amount of accessory gland secretion is depleted from the glands after 30 min of copulation.     

STRUCTURE OF THE PEAR LEAF CUTICLE WITH SPECIAL REFERENCE TO CUTICULAR PENETRATION

Study of the pear leaf cuticle (Pyrus communis L. ‘Bartlett‘), in both intact and enzymatically isolated forms, has revealed that the cuticular membrane is separated from the underlying epidermal cell wall by a layer of pectic substances which extend into but not through the membrane. A layer of embedded birefringent waxes occurs towards the outer surface of the cuticular membrane. Platelet-like epicuticular waxes are deposited on the outer surface. The upper cuticular membrane is astomatous. The lower epidermis is stomatous, and the outer cuticular membrane is continuous with that lining the substomatal cavity. The lower cuticular membrane is also generally thicker than the upper, and both the upper and lower cuticular membranes are thicker over veinal than over mesophyll tissue. The birefringence frequently is discontinuous over anticlinal walls and over veinal tissue. The lower cuticle appears to contain fewer embedded waxes (as indexed by birefringence) than the upper. Enzymatic isolation of the cuticular membrane from the underlying tissues does not appear to cause any discernible change in structure as viewed with a light microscope. These findings are discussed in light of current knowledge concerning penetration of foliar applied substances into the leaf.     

Source of the host marking pheromone in the egg parasitoid Trissolcus basalis (Hymenoptera: Scelionidae)

After oviposition, Trissolcus basalis females always mark the host's surface, depositing host marking substances for herself and to warn other ovipositing females. The perception of these host marking substances, probably through the antennae, can induce the female to leave and seek healthy hosts. Parasitoid females exposed to conspecific parasitized egg masses left the host egg masses significantly more often than when exposed to non-parasitized egg masses. More egg mass leaving behavior also was observed when the egg masses were treated with Dufour's gland secretion but not when treated with secretion from the common oviducts. The common oviduct has a secretory epithelium that produces electron-dense vesicles, probably containing proteinaceous substances. The secretory cells of the accessory gland, Dufour's gland, contain electron-lucid vesicles, whose secretion appears to be a lipid similarly to that found in pheromone secreting glands. Ultrastructural and behavioral evidence suggests that Dufour's gland is the host marking pheromone source.     

Ultrastructural studies on the secretory cavities ofCitrus deliciosa ten. II. Development of the essential oil-accumulating central space of the gland and process of active secretion

Summary Oil glands ofCitrus deliciosa are multicellular secretory structures, globular to oval in shape, in the centre of which an essential oil-accumulating space is formed. Opening of this space begins from a single cell. It undergoes lysis which later extends to the neighbouring gland cells.Secretory material in form of droplets is produced in plastids, from where it is transported to the parietal cytoplasm of the secretory cells via numerous ER-elements. After fusion of the ER-membranes with the plasmalemma, the exudate reaches the apoplast, through which it is driven to the central cavity of the gland.Peripheral cells of the secretory complex are modified into a protective sheath with thick walls and large vacuoles, while their plastids are differentiated from leucoplasts into typical amyloplasts.     

A pair of rosette glands in the embryo and zoeal larva of an estuarine crab Sesarma haematocheir, and classification of the tegumental glands in the embryos of other crabs

A pair of rosette glands (one of the tegumental glands in crustaceans) is present at the root of the dorsal spine of the thorax in mature embryos of the estuarine crab Sesarma haematocheir. Each rosette gland is spherical, 45-50 microm in diameter. This gland consists of three types of cells: 18-20 secretory cells, one central cell, and one canal cell. The secretory cells are further classified into two types on the basis of the morphology of secretory granules. There are 17-19 a cells, and only one b cell per rosette gland. An a cell contains spherical secretory granules of 2-3 microm in diameter. The granules are filled with highly electron-dense materials near the nucleus but have lower electron-density near the central cell. The secretory granules contained in the b cell have an irregular shape and are 1-1.5 microm in diameter. The density of the materials in the granules is uniform throughout the cytoplasm. The secretory granules contained in both the a and b cells are produced by the rough endoplasmic reticulum. Materials in the granules are exocytotically discharged into the secretory apparatus inside the secretory cell, sent to the extracellular channels in the central cell, and secreted through the canal cell. The rosette gland can be distinguished from the epidermal cells 2 weeks after egg-laying and the gland matures just before hatching. Materials produced by this gland are secreted after hatching and secretion continues through five stages of zoeal larvae. These rosette glands were never found in the megalopal larva. Rosette glands are found in the embryos of Sesarma spp. and Uca spp. In other crabs, tegumental glands are also found at the same position as in the embryo of S. haematocheir, but the fine structure of their glands is largely different from that of the rosette gland. On the basis of the morphology of secretory cells (a-g cell types), the tegumental glands of a variety of crab embryos can be classified into four types, including rosette glands (type I-IV). The function of these tegumental glands is not yet known, but different types of the gland seem to reflect the phylogeny of the crabs rather than differences of habitat.     

An ultrastructural investigation of the hypocerebral organ of the adult Euperipatoides kanangrensis (Onychophora, Peripatopsidae)

The hypocerebral organs of Euperipatoides kanangrensis are a pair of spherical vesicles located ventral to the cerebral ganglia. They develop in the embryo from the most anterior pair of ventral organs, in the antennal segment. The wall of each hypocerebral organ is a dense epithelium of elongate cells with peripheral nuclei. The cytoplasm of the cells includes numerous mitochondria, Golgi bodies and microtubules. The small lumen, located eccentrically within the organ, contains concentrically layered electron-dense material resembling cuticle.Each hypocerebral organ is enclosed by a layer of extracellular matrix continuous with that surrounding the adjacent cerebral ganglion. There are no nerve connections between ganglion and organ, but cellular connections traverse the intervening matrix and could serve as a communication pathway. The ultrastructure of the hypocerebral organs indicates that they are glands.     

Morphology and ultrastructure of the venom glands of the northern pacific rattlesnake Crotalus viridis oreganus

The venom gland of Crotalus viridis oreganus is composed of two discrete secretory regions: a small anterior portion, the accessory gland, and a much larger main gland. These two glands are joined by a short primary duct consisting of simple columnar secretory cells and basal horizontal cells. The main gland has at least four morphologically distinct cell types: secretory cells, the dominant cell of the gland, mitochondria-rich cells, horizontal cells, and “dark” cells. Scanning electron microscopy shows that the mitochondria-rich cells are recessed into pits of varying depth; these cells do not secrete. Horizontal cells may serve as secretory stem cells, and “dark” cells may be myoepithelial cells. The accessory gland contains at least six distinct cell types: mucosecretory cells with large mucous granules, mitochondria-rich cells with apical vesicles, mitochondria-rich cells with electron-dense secretory granules, mitochondria-rich cells with numerous cilia, horizontal cells, and “dark” cells. Mitochondria-rich cells with apical vesicles or cilia cover much of the apical surface of mucosecretory cells and these three cell types are found in the anterior distal tubules of the accessory gland. The posterior regions of the accessory gland lack mucosecretory cells and do not appear to secrete. Ciliated cells have not been noted previously in snake venom glands. Release of secretory products (venom) into the lumen of the main gland is by exocytosis of granules and by release of intact membrane-bound vesicles. Following venom extraction, main gland secretory and mitochondria-rich cells increase in height, and protein synthesis (as suggested by rough endoplasmic reticulum proliferation) increases dramatically. No new cell types or alterations in morphology were noted among glands taken from either adult or juvenile snakes, even though the venom of each is quite distinct. In general, the glands of C. v. oreganus share structural similarities with those of crotalids and viperids previously described.