Caudal Organ Research Articles

Reproductive system of the genus Crasiella (Gastrotricha, Macrodasyida)

Crasiella diplura from Sweden and Crasiella sp. from Italy were studied alive and with transmission electron microscopy (TEM). The two species are simultaneous hermaphrodites and share the same reproductive system lay-out: paired ovaries extend along the posterior part of the intestine and join mid-dorsally, while bilateral, club-shaped testes lie at the sides of the anterior gut, extending as deferentia that fuse on the mid-ventral plane and open into a single pore; gametes mature in a caudocephalic and centripetal direction. The bulky, sac-like, frontal organ is lined by a simple epithelium and lies dorsolaterally to the intestine, on the left side of the body. The spindle-shaped caudal organ is musculo-glandular and is located ventrolaterally to the gut on the right side. It is characterized by the presence of a roughly Y-shaped internal channel that opens into two pores close to each other, which function for the intake and outlet of the (auto)sperm, respectively. The spermatozoa, which are peculiar and similar in the two species, are characterized by a long and complex acrosome consisting of four ultrastructurally distinct regions, three of which find equivalence in other gastrotrich species. The flagellum lacks a striated cylinder. Anatomy and ultrastructure enable us to hypothesize a modality of sperm transfer in Crasiella that is similar to that observed in Macrodasys.

Morphology and function of reproductive organs in Neodasys chaetonotoideus (Gastrotricha: Neodasys) with a phylogenetic assessment of the reproductive system in Gastrotricha

The reproductive system of the important basal gastrotrich Neodasys chaetonotoideus is described and reconstructed on the basis of light microscopy, serial ultrathin sections (ultrastructure) and scanning electron microscopy. Starting frontally, the hermaphroditic reproductive system consists of paired and tube shaped lateral testes that do not possess elongated seminal ducts but most likely open directly via paired ventral pores. The unpaired, medio‐dorsal ovary region contains early oogenic stages that mature caudally towards the uterus region, where the most mature egg is positioned laterally to the midgut. The ovary region is not covered with an epithelial lining whereas the uterus region possesses a distinct epithelial wall. Between ovary and uterus region, we have detected a conspicuous section of the female gonad, the vitellogenic oviduct that consists of a thick epithelial wall which forms cellular protuberances into the developing oocytes passing the oviduct. We interpret this as a special, hitherto undescribed mode of vitellogenesis in Gastrotricha. Further caudally, the uterus continues with the fronto‐caudal organ, a complex of two substructures that are apparently homologous to the frontal organ and the caudal organ of many species of the Gastrotricha Macrodasyida. Neodasys chaetonotoideus obviously engages in spermatophore formation and transfer. In this study we develop a morpho‐functional scenario for the gonads and accessory organs in terms of spermatophore production, exchange and oviposition.We compare our newly obtained data with already published results on the reproductive organs of several species of Gastrotricha by means of a species‐character matrix and provide a computer aided evaluation by a parsimonious character optimization. A reconstruction of the reproductive system of the stem species of Gastrotricha on the basis of three recent phylogenetic analyses is presented. These reconstructions give support for a Neodasys‐like reproductive system in the ground pattern of Gastrotricha with slight morphological differences and direct transfer of spermatozoa rather than spermatophore transfer. The evolution of selected characters is traced thus revealing some incidents of convergent evolution as well as the evolutionary replacement of the ancestral frontal organ by the derived frontal sac in at least two separated lineages.

Malvinia crassa gen. n., sp. n. (Nematoda: Drilonematoidea) – a parasite of the acanthodrilid earthworm, Notiodrilus bovei, from the Falkland Islands

AbstractA new species and genus of nematodes (Ungellidae, Drilonematoidea) parasitic in the coelomic cavity of Notiodrilus bovei deposited in the collection of the Museum für Naturkunde in Berlin, is described and illustrated. Malvinia crassa gen. n., sp. n. is characterised by its short, bloated, curved body tapering to both ends, paired, superficially attached cephalic hooks, short infundibular stoma, a pharynx comprising a pre-corpal bulb-like swelling, procorpus, isthmus and basal bulb, nerve ring encircling isthmus, excretory pore located posterior to the nerve ring, weakly cuticularised excretory duct, vulva, slightly post-median, short precloacal process in males, large grain-like spermatids, sperm in spermatheca ball-shaped, ca 20 μm diam., composed of smaller particles resembling spermatids; symmetrically placed, large, fimbriate caudal organs lacking a cavity, and absence of amphids, cephalic and male cloacal sensilla and post-uterine sac. Malvinia gen. n. is differentiated from all genera of the Ungellinae on the basis of its small size, vesiculate vs vermiform body shape, very long reflexed portion of testis and highly modified sperm. From the closest species of the genus Ungella, the new species differs by the presence vs absence of a stoma and pre-corpal swelling of the pharynx, structure of fimbriate caudal organs, larger spermatids in male and sperm in female spermatheca, and absence of lateral differentiation of the cuticle. A key to the genera of Ungellinae is proposed.

Scirtes hemisphaericus uses macrophyte snorkels to pupate under water. With notes on pupae of additional European genera of Scirtidae (Coleoptera)

Morphological and behavioural adaptations enable Scirtes hemisphaericus to pupate under water, using emergent macrophytes as snorkels to breathe atmospheric air. The last instar larva bites into emergent macrophytes until the aerenchym is exposed. The pupa pushes its fore body into the wound, becoming surrounded by an air film in continuity with intracellular and atmospheric air. The pupa lacks normal ecdysial sutures, instead, its cuticle ruptures between the pro- and mesothorax. The fore body cuticle remains in place, preserving the connection to atmospheric air for the immature beetle. Pupation in earthen cells is known only in Elodes. Several other genera pupate under some cover, or freely exposed. Most pupae have 2–4 horn-like pronotal processes and 2–4 caudal attachment organs which differ between genera and sexes. Hydrocyphon (which pupates under water) and S. hemisphaericus pupae lack pronotal horns and attachment organs.

Immunohistochemical localization of nanog and Oct4 in stem cell compartments of human sacrococcygeal teratomas

To study the range of differentiation and presence of cells positive for stem cell markers in 20 sacrococcygeal teratomas (SCTs) which were consecutively operated on between 1990 and 2000 in the Department of Paediatric Surgery in Tübingen, Germany. Preserved paraffin-embedded material was re-evaluated. In addition to tissues of various organs, caudal organ structures not described before were identified, such as colon with pancreas originating from colonic crypts, Fallopian tube and vaginal epithelia. The derivation of the latter was confirmed by Müllerian duct specific CA125 and CA19-9 antibodies. The expression of stem cell markers was studied with antibodies against nanog, Oct4, SSEA-4, nestin and subtype M3 muscarinic receptors. Cells positive for these markers were encountered in immature end buds and capillary sprouts, and as single cells in neural tissue, gonadal structures, hairs and in the stem cell niches of differentiated epithelia. Our data indicate that SCTs of the newborn arise from remnants of the epiblast-like tail bud blastema and demonstrate that they contain cells positive for embryonic stem cell markers and may represent a novel source for human embryonic stem cells.

Anatomy and ultrastructure of the reproductive organs in Dactylopodola typhle (Gastrotricha: Macrodasyida) and their possible functions in sperm transfer

Abstract. The reproductive anatomy of gastrotrichs is well known for several species, especially for the marine taxon Macrodasyida. However, there is little information on the reproductive organs and the modes of mating and sperm transfer in putative basal taxa, which is necessary for accurate reconstruction of the ground pattern of the Gastrotricha. We present the first detailed morphological investigation of the reproductive system of a putative basal gastrotrich, Dactylopodola typhle, using transmission and scanning electron microscopy, histology, and microscopic observations of living specimens. Dactylopodola typhle is a hermaphrodite that possesses paired female and male gonads, an unpaired uterus with an outlet channel that we call the cervix, and an additional accessory reproductive organ, the so‐called caudal organ. We hypothesize that the hollow, secretory caudal organ serves for picking up autospermatozoa (self‐sperm), for spermatophore formation, and finally for transferring the autospermatophore to a mating partner. The allospermatophore (foreign spermatophore) is stored within the uterus where fertilization occurs. We think that the mature and fertilized egg is released through the cervix and the dorsolateral female gonopore, and not by rupture of the body wall. Based on the morphology, we provide a plausible hypothesis for spermatophore formation and transfer in D. typhle. Preliminary phylogenetic considerations indicate that the stem species of Macrodasyida, perhaps that of all Gastrotricha, had paired ovaries and paired testes, an unpaired uterus, and only one accessory reproductive organ.

A new species of Pseudostomella (Gastrotricha: Macrodasyida: Thaumastodermatidae) from a sandy beach of Kerala, India

During an interstitial faunal survey along the south-west coast of Kerala, India, gastrotrich fauna were found in abundance. Together with species of the genera Xenotrichula, Halichaetonotus and Tetranchyroderma, were present several undescribed thaumastodermatid gastrotrichs belonging to the buccal palp bearing genus Pseudostomella. Adults of the new species are characterized by the following traits: total body length of about 300 μ m; cuticular armature made up of medium sized pentancres covering the entire dorsolateral surface; pre-buccal, grasping palps bearing five, large papillae dorsally and 4-6 smaller papillae ventrally; adhesive apparatus made up of six anterior, 22-24 ventrolateral, two dorsolateral and six posterior adhesive tubes; caudal organ pear-shaped; frontal organ spherical. Pseudostomella cheraensis sp. nov. is the fourth taxon of the genus known from India; however, all the previous species reported hitherto from India have tetrancres instead of pentancres.

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A new inseminating fish species of the family Characidae, Bryconadenos tanaothoros, from tributaries of the upper rio Xingu and upper rio Tapajós basins, Mato Grosso, Brazil is described as the type species of a new genus. This new species and the genus are characterized by a glandular organ on the anterior region of the anal fin of sexually mature males, curved lower jaw teeth, and an inseminating reproductive mode. This new genus is hypothesized as most closely related to Attonitus, a genus with three inseminating species from Peru. Bryconadenos and Attonitus are suggested as related to certain inseminating, but undescribed characid species of uncertain relationships that are similar in certain respects to species of the glandulocaudine Planaltina and to the inseminating species of Knodus. These and a few other inseminating characids are included in a previous tentative characid subgroup designated as Clade A. No species among a relatively small sample of the many species of the Clade A genus Bryconamericus were found inseminating, except Bryconamericus pectinatus. However, newly collected specimens of B. pectinatus were found to have caudal-fin squamation like that of the species of Knodus and this species is here tentatively referred to Knodus. Our investigations indicate that at least several species of Knodus, including the type species, Knodus meridae, are not inseminating, but we found two inseminating apparently new characid species that currently would be referred to Knodus. These species lack the derived anal-fin rays present in the males of K. pectinatus. Other Clade A taxa known to be inseminating, such as two species of the large genus Creagrutus, three species of Monotocheirodon (two undescribed), and the species and genera of the characid subfamily Glandulocaudinae are briefly discussed regarding possible relationships to Attonitus and Bryconadenos. The anatomical aspects of the primary and secondary sexual characteristics of Bryconadenos and Attonitus are discussed in relation to certain other inseminating characids, such as the species of Brittanichthys and Hollandichthys, that are not currently hypothesized to belong to Clade A and presumably acquired insemination independently. It is concluded that much additional data regarding the reproductive modes as well as other anatomical/physiological systems of characids currently included in and excluded from Clade A are necessary before a reasonably supported phylogeny of Clade A characids and their possible outgroup relatives can be advanced. The anal-fin gland cells of sexually active male Bryconadenos specimens are histologically indistinguishable from club cells (also called alarm substance cells) found within the skin of cypriniforms, characiforms, catfishes, and other otophysan fishes. These cells occur at the skin's surface of the anal-fin gland in male Bryconadenos where they are organized into an organ. Many other adult male characids have club cells at the anal-fin's skin surface, often associated with anal-fin hooks, but were not found organized into an organ as in Bryconadenos. We hypothesize these cells to secrete a pheromone during courtship via holocrine secretion. Males of the genera Lophiobrycon , Glandulocauda, and Mimagoniates, tribe Glandulocaudini, were found to have club cells associated with their caudal-fin organ, but no specialized mucus cells were present as found in the caudal organ of males of the glandulocaudine Corynopoma riisei, tribe Stevardiini (= Corynopomini of past authors). In this species, males have hypertrophied mucus cells hypothesized to be modified for pheromone secretion. Evidence that the derived scales and fin rays of the caudal organ of males of the tribe Glandulocaudini are not homologous with that of other tribes of the Glandulocaudinae, as this subfamily was previously recognized, is discussed and it is concluded that the members of the tribe Glandulocaudini should be recognized as a separate subfamily, the Glandulocaudinae, with possible close relationships to some other Clade A inseminating characids that lack caudal-fin organs. The remaining tribes of the former Glandulocaudinae are here included in the subfamily name Stevardiinae. Many species of these two subfamilies and some of the other inseminating Clade A characids have modified sperm cells with an elongate "binding"cytoplasmic collar and mitochondria located along and beyond the nucleus. This may be an indication of a relationship at a unique level within Clade A characids. However, further research on the derived nature and homology of the sperm cells within inseminating Clade A characids and of the caudal organs of the tribes of the Stevardiinae must be undertaken in order to utilize sperm cell features as characters for studying phylogeny. Finally, the kinds of secretory cells and gross anatomical structures in the tail organs of the stevardiine tribes need detailed research in order to better present hypotheses of phylogeny for the tribes of the Stevardiinae as well as all inseminating Clade A characids.

New genera and species of nematode parasites (Drilonematoidea: Ungellidae) from coelomic cavity of Neotropic acanthodrilids deposited in the Natural History Museum of Geneva, Switzerland

Two new genera and two new species of nematodes (Ungellidae, Drilonematoidea) parasitic in Neotropic acanthodrilids from the collection of the Natural History Museum of Geneva, Switzerland, are described. Yagansiella longicollis gen. n., sp. n. and Ungella chileana sp. n. are parasitic in Yagansia spatulifera, whereas Ungella micronychium sp. n. in Y. diversicolor and Patagoniella capitoporus gen. n., sp. n. in Y. papillosa. Yagansiella longicollis gen. n., sp. n. resembles Ungella in general morphology but differs by anterior position of ovary top cell and posterior vulva position, characteristic body and caudal fimbriate organs shape. U. chileana sp. n. is distinguished by large circular fimbriate organs in tail, female body shape and arrangement of female genital tube and spicule shape. Ungella micronychium sp. n. differs by minute cephalic hooks and shape of fimbriate organs and spicules and gubemaculum. Patagoniella capitoporus gen. n., sp. n. is distinguished by anteriormost position of excretory pore, anterior vulva position and shape of fimbriate organs and spicules and gubemaculum.

Two new nematode genera (Rhabditida: Drilonematoidea) from earthworms

Abstract Two new genera of Drilonematoidea from earthworms deposited in the collection of the Smithsonian Institution's Natural History Museum are described. Acanthungella africana gen. n., sp. n. (Ungellidae) was found parasitic in the coelomic cavity of Millsonia nigra Beddard, 1894 and Araguanema venezuelae gen. n., sp. n. (Drilonematidae) was found in the coelomic cavity of Rhinodrilus sp. Acanthungella africana gen. n., sp. n. is closely related to Ungella Cobb, 1928, but distinguished from it and the rest of the ungellid genera by having a series of numerous sublateral sensilla through the length of the body. Araguanema venezuelae gen. n., sp. n. is similar to two other monotypic drilonematid genera, namely Diceloides Timm, 1967 and Mbanema Spiridonov, 1992, in having vesicular sensory organs. Araguanema gen. n. can be distinguished from Diceloides by the number and position of lateral fimbriate and vesicular sensory organs; the nerve ring located around the isthmus of the pharynx vs at the pharyngo-intestinal junction; a single ovum in the uterus vs more than 100 ova; presence vs absence of an excretory duct; long fibres protruding from the anal aperture vs the absence of such fibres; and by the absence vs presence of a spermatheca. Araguanema gen. n. differs from Mbanema in having a cylindrical vs a clavate pharynx, and by the presence of anterior and caudal fimbriate organs vs caudal only.

Marine gastrotrich fauna in Corsica (France), with a description of a new species of the genus Tetranchyroderma (Macrodasyida, Thaumastodermatidae)

A faunistic analysis of the sandy sediment collected from 10 locations along the east (four) and west coasts (six) of Corsica, western Mediterranean Sea, yielded a rich and diverse range of gastrotrichs: 42 species of 18 genera and seven families from the orders Chaetonotida (17 species) and Macrodasyida (25 species). Sublittoral samples were always more species-rich than those from littoral sites; 37 versus nine spp. The gastrotrich fauna from the east coast was more diverse than that from the west coast, both in terms of the total species number (35 spp.: 13 Chaetonotida ‡ 22 Macrodasyida versus 23 spp.: 12 Chaetonotida ‡ 11 Macrodasyida) and the number of species per location (13 §4.2 versus 7.5§ 4.0). All but three of the species have previously been reported from other Mediterranean locations. The exceptions are two as yet unidentieed species of the genera Cephalodasys and Macrodasys, and Tetranchyroderma inaequitubulatum sp. nov., a thaumastodermatid with pentancrous covering, showing a cluster of ventral adhesive tubes peculiarly located only on the right side and an unusually conspicuous sexual caudal organ. Aspidiophorus paramediterraneus, Chaetonotus apechochaetus, Acanthodasys aculeatus, Paraturbanella teissieri, Pseudostomella etrusca and Tetranchyroderma thysanophorum, present at 50% or more of the investigated locations, are the most common species on the third largest island of the western Mediterranean basin.

Morphology of the reproductive system and spermatozoa of Mesodasys adenotubulatus (Gastrotricha: Macrodasyida)

Mesodasys adenotubulatus Hummon, Todaro and Tongiorgi 1993 is a simultaneous hermaphrodite. Two club-shaped testes extend along the sides of the anterior intestine and show spermatogenetic stages maturing in a caudo-cephalic and centripetal direction. Sperm ducts join together dorsally to the intestine before opening into a pear-like caudal organ. An unpaired, dorsal ovary lies anteriorly to the confluence of sperm ducts. Oocytes mature in a caudo-cephalic direction; no oviduct nor female pore is present. The spermatozoa are fusiform, with a very short tail. The anterior end of the sperm is a small, conic hood which corresponds to the acrosome. The following, spindle-shaped corkscrew region contains a nuclear helix surrounding a central axis made of a single, giant mitochondrion. The 9+2 axoneme is enclosed by a bilayered, obliquely striated cylinder only in the proximal tract. The morphology of the reproductive system and spermatozoa of Mesodasys species is discussed, and the hypothesis of hypodermic impregnation in this genus is supported.

Two new species of Urodasys (Gastrotricha, Macrodasyidae) with cuticular stylet

Most species of Urodasys bear a clearly structured cuticular stylet in the caudal organ, that constitutes a powerful diagnostic feature. On the basis of the morphology of this stylet, two new species, Urodasys acanthostylis and U. uncinostylis, are described. Urodasys acanthostylis is diagnosed by a stylet with the tubular portion clearly bent at a slightly obtuse angle, U. uncinostylis by a stylet with the tubular portion which develops in about one and a half coils. The former was found along the Apulian coast (southern Italy) and in Malta, and the latter at the Maldives.

Luminescent properties of fishes from nearshore California basins

Bioluminescence flash kinetics and quantum emissions of specimens of 10 species of fishes from the families Astronesthidae, Malacosteidae, Melanostomiatidae, Myctophídae, Stomiatidae and Sternoptychidae were determined. Fish were collected from the San Clemente and Santa Catalina basins of the Southern Californian Bight. Body photophores emitted long-lasting glows with peak photon fluxes to 3.0 × 10 10 photons · s −1. Caudal luminescent tissues exhibited both discrete flashes and spontaneous trains up to 30 Hz with average flash duration from 43 to 79 ms and peak photon fluxes of 2.2 × 10 12 photons · s −1. Orbital photophore displays persisted up to 1415 ms with a maximum emission rate of 1 Hz and a maximum photon flux of 7.5 × 10 11 photons · s −1. The flash kinetics and quantum intensity of the oral light organs from Stemoptyx diaphana Hermann are quantified for the first time. The flash durations of myctophid caudal organs were significantly shorter compared with congeners from Hawaiian waters, indicating that regional environmental conditions may account for shorter flash duration.

Vasoactive material present in the glomerula caudalia of the Vervet monkey.

Complex encapsulated neurovascular structures, glomus organs, occur in superficial and deep positions in many species. No direct evidence for their function exists. In skin they may serve thermoregulation by the reason for their structural complexity remains obscure. The concept of a local humoral circulatory control mechanism postulated on the basis of a very high acetylcholine content reported for human glomera coccygia has been investigated in homologous caudal glomus organs in monkey. No acetylcholine was detected. The organs contained 3-4 times the concentration of catecholamine (mainly noradrenaline) found in nearby vessels. Neither structure nor content of vasoactive component gives any support for an endocrine function.

The reproductive system of Gastrotrichs

A structural, ultrastructural and functional analysis is made of genital organs ofMacrodasys, a member of the hermaphroditic marine Gastrotricha. The gonads are paired, hermaphroditic and polarized into male and female regions. Male and female gametes are produced simultaneously. Fertilization is internal. Accessory organs consist of, from anterior to posterior, simple male pores, a seminal receptacle and spermatheca, and, a complex caudal organ. Copulation results in reciprocal cross insemination. Sperm transfer, however, is indirect. Autosperms are transferred externally from the male pores to the caudal organ while the animals are in copula. The caudal organ then functions as a penis conducting the autosperms into the partner's seminal receptacle. This unique mode of sperm transfer is discussed with reference to the lower Bilateria and the Metazoa.

The Reproductive System of Gastrotrichs. I Introduction with morphological data for two new Dolichodasys species1

This paper begins a series aimed at clarifying the structure and function of reproductive organs in Gastrotricha Macrodasyida. Morphological data are presented for Dolichodasys carolinensis sp.n. and D. delicatus sp.n. Both are elongate, have reduced adhesive organs and complex accessory reproductive organs, termed the frontal‐caudal organ system. The system consists of a band of cells behind the gonads in the central body chamber. The anterior portion, the frointal organ, stores foreign spermatozoa; the posterior portion, the caudal organ, may function as a copulatory organ. The caudal organ has two canals forming a loop opening at a single ventral pore. One canal contains a spiralled secretion, the other elongated filaments that appear to be muscle cell derivatives. Systematic groupings are made for other long‐bodied Gastrotricha Macrodasyida.

Observations on the comparative morphology and operation of the photogenic tissues of myctophid fishes

Lanternfishes (Myctophidae) often bear not only small primary photophores, but also larger regions of luminous tissue, described as glands or patches. These have a superficial appearance very different to that of the primary photophores, but examination of the tissues of some 14 genera has shown that all the luminous organs are composed of fundamentally similar stacks of photogenic lamellae. The degree of organisation of the lamellae varies in different genera, but the caudal organs and the other larger luminous regions contain much more of this photogenic tissue than do the primary photophores. Some observations on the operation of both primary and caudal organs are described.

Hesiolicium gen.n. (Turbellaria Acoela) and Observations on Its Ultrastructure

AbstractCrezée, M. (University of Florida Marine Laboratory, Gainesville, FL 32611, USA) and Tyler, S. Hesiolicium gen.n. (Turbellaria Acoela) and observations on its ultrastructure. Zool. Scr. 5 (5): 207–216, 1976. —Hesiolicium inops gen.n., sp.n. is a thin and elongate protandric hermaphrodite from the marine interstitial environment. The male pore, with no accessory organs, lies just posterior to the mouth, with no pharynx. The dorsal ovary, lateral testes, adhesive papillae and a caudal organ are other features. The posterior and midventral adhesive papillae are bundles of haptocilia up to 22 μm long. In a crook near their base these adhesive cilia have three microtubule doublets displaced from the rest of the axoneme, giving the crook region a figure‐eight cross section. The caudal organ is a complex of cilium‐bearing sensory cells, large gland cells and modified muscle and epidermal cells. The rootlets of epidermal cilia and the two axial units of the sperm are as described for other acoels. Principally because of the haptocilia, Hesiolicium is provisionally placed in the Paratomellidae.

The luminescence of lanternfish (myctophidae): Spontaneous activity and responses to mechanical, electrical, and chemical stimulation

Spatial and temporal aspects of luminous responses in several common species of Southern California lanternfish (Myctophidae) were analyzed using T.V. image intensifier and photomultiplier techniques. The two principal types of luminous tissue, photophores and luminous tissue patches, responded in strikingly and consistently different ways to both mechanical and electrical stimulation. While typically producing a variable intensity glow spontaneously, the entire photophore array proved capable of coordinated, simultaneous activation by electrical stimulation. Although never active in undisturbed shipboard animals, luminous tissue patches, primarily, supra- and infracaudal organs, produced brilliant, rapid, transient displays to both mechanical and electrical stimulation. Light from the supra- and infracaudal organs is produced by 3–9 visually distinct subunits capable of both simultaneous and temporally variable activation. Electrical excitation gave maximum response rates of up to 30 flashes/sec in the luminous patches of all the species tested, whether tissue was from caudal organs or ventral or supraorbital patches. Chemical stimulation never triggered luminous responses from luminous tissue patches, and gave only ambiguous results with photophores. The results are discussed in terms of effector control and functional potential of the various luminous displays.