Dorsal Arm Research Articles

Retinal mosaics of the principal eyes of jumping spiders (Salticidae) in some neotropical habitats: optical trade-offs between sizes and habitat illuminances

1. The anatomy and geometrical optics of the principal eyes of some neotropical jumping spiders are examined, with particular reference to the receptors of Layer I of the tiered retina. The consequence of small size and of low habitat illuminances for spatial acuity are assessed. 2. In all phylogenetically advanced salticids examined in the present study, a foveal Layer I receptor contains a single rhabdomere organised as a light-guide. The following sections discuss Layer I: 3. For open-space species, small size minimally prejudices spatial acuities: for the very largePhiale magnifica, optimal spatial acuity is estimated to be 2.3 arc min for adults, and 4.6 arc min for second-instar spiderlings. For adults of the small speciesJollas geniculatus (only slightly larger than second-instarPhiale) we obtain 5.2 arc min. 4. For species occupying habitats in the forest understory, low illuminances appear to prejudice spatial acuity. For adults of the large speciesItata completa which lives beneath broad foliage, we obtain 5.8 arc min; for the small ant-mimicFluda princeps which inhabits the litter layer, we estimate 16.8 arc min. 5. The results indicate that habitat illuminance only constrains retinal design when it is extremely low. Impaired spatial acuities in such dark habitats are predicted to limit behavioural repertoires, and, as a secondary consequence, the number of species that can co-exist in a given forest microhabitat. 6. Receptor illuminances could, in principle, be modulated by adjustments to four factors: (i) focal lengths of the corneal lenses; (ii) the extent, or absence of the pigment stops that lie directly behind them; (iii) the magnification factors afforded by the diverging components of the telephoto lens systems; (iv) the tip diameters of foveal Layer I rhabdomeres. The first parameter is not manipulated: all corneal lenses have roughly the sameF-number (≃ 1.80). Forest species usually lack a pigment stop behind the corneal lens, the power of the diverging component is reduced or virtually absent, and rhabdomere diameters are large. 7. The interface between the retinal matrix and the anterior chamber of the eye is irregularly convexiclivate in advanced salticids, two convexiclivate surfaces forming “saddles” that overlie the narrow dorsal and ventral arms of the retinal mosaics. It is confirmed that inPortia andLyssomanes, both from “primitive” subfamilies, the interfaces are not convexiclivate, as Williams and McIntyre (1980) noted.

The reproductive biology of deep-sea forcipulate seastars (Asteroidea: Echinodermata) from the N.E. Atlantic Ocean

Samples of the deep-sea forcipulate seastarsBrisinga endecacnemos, Brisingella coronata, Freyella spinosaandZoroaster fulgenshave been collected at a number of stations in the N.E. Atlantic. Examination of their reproductive biology suggests subtle interspecific variations in their gametogenic cycles. The gonads ofBrisinga endecacnemosare serially arranged under the dorsal arm surface, each cluster of gonad tubules having its own gonopore. In the closely relatedBrisingella coronataeach gonad consists of up to 12 elongate tubules opening at a single gonopore at the dorsal surface. In both species the maximum egg diameter is about 1250 μm and fecundity may be up to 60000 eggs per individual. It appears that the eggs inBrisinga endecacnemosare produced in clusters whilst those ofBrisingella coronataare produced continuously. InFreyella spinosathe gonad consists of a small tubular sac analogous to a single tubule ofBrisinga endecacnemos.Maximum fecundity is only 2500 eggs per individual, and the maximum egg size is 1250 μm. In all three species eggs that are not spawned undergo internal oocyte degeneration. The gonads ofZoroaster fulgensshow the typical asteroid configuration of two at the base of each arm, one either side of the ambulacrum. The maximum oocyte diameter is 950 μm. There is some evidence that there may be a seasonality of reproduction in this species. In all four species examined the large egg size and relatively low fecundity suggest direct demersal development with the subtle variations in their reproductive biology reflecting slightly different breeding habits.

Structure of the Honeybee Tentorium

SummaryThe honeybee (Apis mellifera) tentorium, primarily an endoskeletal framework for support of the cranial wall and muscle attachment, comprises a pair of anterior tentorial arms, a pair of posterior tentorial arms, a non-rigid pair of dorsal tentorial arms, a posterior transverse tentorial bridge, and a pair of posteroventral tentorial arms that parallel the bridge above. Study of the tentorium revealed that all arms of this structure and the bridge are cannular (hollow) or tubular. The tips of the dorsal tentorial arms were found to be highly modified, porous and sandwiched between the ocular lobe and the antennal nerve. What appeared to be a neuron bundle was found on the outer lateral side of the anterior tentorial arm near the anterior tentorial pit. The cannular nature of the tentorium and its structure suggest the possibility of sensory involvement.

The larval head of Agathiphaga (Lepidoptera, Agathiphagidae) and the lepidopteran ground plan

Abstract. The larval head of Agathiphaga vitiensis is described. There is a complete hypostomal bridge but no hypostomal ridges. Adfrontal ridges and distinct ecdysial lines are absent. There are two vestigial stemmata (without lenses) on each side. The antenna is one‐segmented. All ‘typical lepidopteran’ head setae have been identified. The corporotentorium is very slender; dorsal tentorial arms are present. Intrinsic labral muscles are lacking. The mandible has retained a tentorial muscle. The maxilla is without a discrete cardo and has but a single endite lobe; ‘intrinsic maxillary muscles’ and the ‘cranial flexor of the dististipes’ are lacking. The postlabium is undivided and without setae, the labial palp is one‐segmented and the lateral prelabio‐hypopharyngeal sclerotization is continued into an oral arm. Some of the ventral pharyngeal dilators arise on the tentorium; mouth‐angle retractors and dorsal post‐cerebral pharynx dilators are absent. The two brain lobes have almost parallel long axes and are united by a narrow (almost pure neuropile) bridge. The corpora cardiaca and callata are contiguous. The aorta is an open gutter in front of the retrocerebral complex.Available evidence on the ground plan structure of the lepidopteran larval head is reviewed. The ancestral head supposedly was prognathous and was autapomorphic in having the cranio‐cardinal articulation far behind the mandible; it had a complete hypostomal bridge but neither hypostomal nor adfrontal ridges, its tentorium was probably stout and with dorsal arms. Paulus & Schmid (1978, Z. zool. Syst. EvolForsch. 16) described a lepidopteran/trichopteran synapomorphy in stemma structure. A tentative table of homologies between cranial setae in Lepidoptera and Trichoptera is presented; it differs considerably from the scheme of Williams & Wiggins (1981, Proc. 3rd Symp. Trichopt.). The mouth parts and their musculature must have been overall very primitive for a panorpid larva, but the number of maxillary palp segments was reduced (three). The ‘dististipes’sensu Hinton is considered to consist of complexly fused parts of the stipes and basal palp segments. The cephalic stomodaeum must have possessed all primitive groups of extrinsic muscles. The incomplete available information on Micropterigidae impedes reconstruction of some details of the lepidopteran ground plan.Larval head structures support the monophyly of an entity comprising the Agathiphagidae + Heterobathmiidae + Glossata. There is one suite of derived characters shared by Heterobathmiidae and Agathiphagidae only and another shared by Heterobathmiidae and the Glossata only; one of these must represent parallelisms.

Nuclear organization of the bullfrog diencephalon.

A cytoarchitectonic analysis was performed on the diencephalic nuclei of the bullfrog, Rana catesbeiana. The epithalamus contains two widely recognized habenular nuclei. The thalamus has three subdivisions: dorsal and ventral thalamus, and posterior tuberculum. The dorsal thalamus may be further parcelled into anterior, middle, and posterior zones. Connectional data from other studies support this zonation. The anterior zone projects to the telencephalic pallium. The middle zone nuclei receive a strong input from the midbrain roof and project to the telencephalic striatal complex. The posterior zone nuclei do not appear to project to the telencephalon; they may eventually be placed in the pretectum, a transitional area between the diencephalon and mesencephalon. Two of the ventral thalamic populations have been frequently placed in the dorsal thalamus and called the nucleus rotundus and the lateral geniculate nucleus. These terms imply homology with sauropsid dorsal thalamic nuclei, but our analysis and current connectional information do not support such homologies. We have given these populations more neutral names. The hypothalamus is divisible into a preoptic and infundibular hypothalamus, and the preoptic area can be further separated into anterior and posterior preoptic areas. The posterior area contains the magnocellular preoptic nucleus and a dorsal arm of this nucleus, often placed in the ventral thalamus, was recognized. We have tentatively placed the posterior entopeduncular nucleus in the hypothalamus.

The reproductive biology of Plutonaster Bifrons, Dytaster Insigns and Psilaster Andromeda (Asteroidea: Astropectinidae) from the Rockall Trough

Examination of the reproductive biology of three closely related sympatric astropectinid asteroidshas revealed two distinct reproductive strategies. In Plutonaster bifrons and Dytaster insignis the gonads are serially arranged and open at gonopores located at the tip of genital papillae found on the dorsal arm surface between the bases of the paxillae. The ovaries of these species produce numerous small (ca. 120/«n diameter) eggs which in Plutonaster bifrons appear to show a distinct synchrony of production. Initiation of gametogenesis occurs in June to August of each year with oocyte growthcontinuing until March with a spawn-out in the period March to early June. In specimens where spawningdoesnot occur, there would appear to be internal oocyte degeneration, or after spawning relict oocytesundergo phagocytosis. In males initiation of spermatogenesis may occur in August/September of eachyear but after this synchrony of sperm development is not evident. In Psilaster andromeda gonads are located at the base of the arms and each gonad opens at a single gonopore. A number of small (<300 /«n) oocytes are produced by each gonad. Some of these are phagocytosed and some undergo vitellogenesis and grow to a maximum size of 950 fim before being spawned. Unspent oocytes undergo internal degeneration. In neither females nor males is there any evidence of reproductive synchrony. From these egg sizes, fecundities and gametogenic strategies, we infer indirect planktotrophic development for Plutonaster bifrons, the transfer of a seasonal surface production to deep water providing a food source for developing larvae. The egg size and or close to the sea-bed, as there is no evidence of brooding in this species.

The reproductive biology ofPlutonaster Bifrons, Dytaster InsignsandPsilaster Andromeda(Asteroidea: Astropectinidae) from the Rockall Trough

Examination of the reproductive biology of three closely related sympatric astropectinid asteroidshas revealed two distinct reproductive strategies. In Plutonaster bifrons and Dytaster insignis the gonads are serially arranged and open at gonopores located at the tip of genital papillae found on the dorsal arm surface between the bases of the paxillae. The ovaries of these species produce numerous small (ca. 120/«n diameter) eggs which in Plutonaster bifrons appear to show a distinct synchrony of production. Initiation of gametogenesis occurs in June to August of each year with oocyte growthcontinuing until March with a spawn-out in the period March to early June. In specimens where spawningdoesnot occur, there would appear to be internal oocyte degeneration, or after spawning relict oocytesundergo phagocytosis. In males initiation of spermatogenesis may occur in August/September of eachyear but after this synchrony of sperm development is not evident. In Psilaster andromeda gonads are located at the base of the arms and each gonad opens at a single gonopore. A number of small (<300 /«n) oocytes are produced by each gonad. Some of these are phagocytosed and some undergo vitellogenesis and grow to a maximum size of 950 fim before being spawned. Unspent oocytes undergo internal degeneration. In neither females nor males is there any evidence of reproductive synchrony. From these egg sizes, fecundities and gametogenic strategies, we infer indirect planktotrophic development for Plutonaster bifrons, the transfer of a seasonal surface production to deep water providing a food source for developing larvae. The egg size and or close to the sea-bed, as there is no evidence of brooding in this species.

Senile Purpura

We studied senile purpura in 18 male subjects by calculating a half-life for intradermally injected autologous red blood cells (RBC) which had been labelled with sodium chromate Cr 51. There was no difference in half-life between the dorsal arm and ventral arm in elderly subjects who had spontaneous purpura on their dorsal arms. We found no difference between RBC halflife in older subjects and younger ones. The rate of removal was not altered by occlusion with tapes, ultraviolet light-induced erythema, or ingestion of bromelains. Histologic studies on biopsy specimens of induced purpuric lesions showed similar findings in both the older and the younger subjects.

Studies on the receptors in the cerebral vesicle of the ascidian tadpole. 2. The ocellus

ABSTRACT Electron microscope observations of the photoreceptor of the tadpole larva of Ciona intestinalis show the ocellus to consist of about 10 cells. It is made up of 3 parts: a pigment cup, a lens system, and a retina. A single cup-shaped cell filled with membrane-bound pigment granules lies between the lens and the retinal cells. Part of the lens cell is contained within its concavity. The pigment granules are arranged to keep stray light from falling upon the photoreceptor endings. The lens system has 3 lens vesicles arranged in a line along the main axis of the pigment cup cell. The spherical vesicles are usually contained within a single cell. Each vesicle is separated from the rest of the lens cell cytoplasm by a single-layered sphere of mitochondria. No membrane separates the vesicle contents from the rest of the lens cell cytoplasm. The retinal cells lie above the dorsal arm of the pigment cup cell, and have tubular processes that pass through it to end as piles of membranes closely applied to the lens cell. Morphologically the photoreceptor units of the ascidian tadpole closely resemble the visual cells of the vertebrates, the piled photoreceptor membrane corresponding to the outer segment of the vertebrate rod cell and the tubular part to the connecting piece of a retinal rod.

Tremoctopus violaceus Uses Physalia Tentacles as Weapons

Immature octopods (Tremoctopus violaceus) have been found with numerous fragments of tentacles of the coelenterate Physalia attached to the suckers of their dorsal arms. The probable method of acquisition, the evidence of adaptation for holding the tentacles, and the possibility that the octopod uses these coelenterate tentacles as offensive and defensive weapons are discussed.

The Curious Anther of Bixa--Its Structure and Dehiscence

available for study. The gross features of the anthers were observed in whole mounts cleared in lactophenol. The structural details were investigated from microtome sections of material imbedded in paraffin and cut at thicknesses ranging from 8-12,u. The sections were stained with Heidenhain's iron-alumhaematoxylin followed by eosin. OBSERVATIONS The large showy flowers contain numerous hypogynous stamens with long and slender filaments. The anthers are dithecous (figs. 1-3) but each of the two thecae is curved like a horse-shoe, whose dorsal arm (d) facing the periphery of the flower, is longer than the ventral (v) facinfg the centre of the flower. As a result of such curvature, the morphological base (b) and apex (a) of the anther are brought close together (fig. 2). The filament is fixed on the shorter side, which is the real base of the anther. The vascular bundle of the filament continues in the anther to form a loop (vl) which extends close to the apex (fig. 3). ABBREVIATIONS

Comparative anatomy of the Mallophagan head.

Comparative anatomy of the Mallophagan head.