The ovipositor is an organ used by some animals for the laying of eggs. In insects an ovipositor consists of a maximum of three pairs of appendages; the details and morphology of the ovipositor vary, but its form is adapted to functions such as transmitting the egg, preparing a place for it, placing it properly. In some insects the organ is used to attach the egg to some surface, but in many parasitic species it is a piercing organ as well. Grasshoppers use their ovipositors to force a burrow into the earth to receive the eggs. Cicadas pierce the wood of twigs with their ovipositors to insert the eggs. Sawflies slit the tissues of plants by means of the ovipositor and so do some species of long-horned grasshoppers. In the wasp genus Megarhyssa, the females have a slender ovipositor several inches long, used to drill into the wood of tree trunks; these species are parasitic in the larval stage on the larvae of horntail wasps, hence the egg must be deposited directly into the host's body as it is feeding.
Impressively, the ovipositor of the giant ichneumon wasp is the longest egg-laying organ known among biologists. The stings of the Aculeata are ovipositors modified and with associated venom glands, they are used as defensive weapons. The penetrating sting plus venom allows the wasp to lay eggs with less risk of injury from the host. In some cases the injection introduces virus particles that suppress the host's immune system and prevent it from destroying the eggs. However, in all stinging Hymenoptera, the ovipositor is no longer used for egg-laying. An exception is the family Chrysididae, members of the Hymenoptera, in which species such as Chrysis ignita have reduced stinging apparatus and a functional ovipositor; some insects, such as the Dipteran families Tephritidae and Pyrgotidae have well-developed ovipositors only retracted when not in use, the part that sticks out is called the scape or oviscape, meaning the stalk of the ovipositor. In the breeding season of some roach-like fish, such as bitterlings, the females have an ovipositor in the form of a tubular extension of the genital orifice.
They use it when depositing eggs in the mantle cavity of the pond mussel, where their eggs develop in reasonable security. Seahorses have an ovipositor for introducing eggs into the brood pouch of the male, who carries them till it is time to release the fry into a suitable situation in the open water
Segmentation in biology is the division of some animal and plant body plans into a series of repetitive segments. This article focuses on the segmentation of animal body plans using the examples of the taxa Arthropoda and Annelida; these three groups form segments by using a "growth zone" to define the segments. While all three have a segmented body plan and use a growth zone, they use different mechanisms for generating this patterning. Within these groups, different organisms have different mechanisms for segmenting the body. Segmentation of the body plan is important for allowing free movement and development of certain body parts, it allows for regeneration in specific individuals. Segmentation is a difficult process to satisfactorily define. Many taxa have some form of serial repetition in their units, but are not conventionally thought of as segmented. Segmented animals are those considered to have organs that were repeated, or to have a body composed of self-similar units, but it is the parts of an organism that are referred to as being segmented.
Segmentation in animals falls into three types, characteristic of different arthropods and annelids. Arthropods such as the fruit fly form segments from a field of equivalent cells based on transcription factor gradients. Vertebrates like the zebrafish use oscillating gene expression to define segments known as somites. Annelids such as the leech use smaller blast cells budded off from large teloblast cells to define segments. Although Drosophila segmentation is not representative of the arthropod phylum in general, it is the most studied. Early screens to identify genes involved in cuticle development led to the discovery of a class of genes, necessary for proper segmentation of the Drosophila embryo. To properly segment the Drosophila embryo, the anterior-posterior axis is defined by maternally supplied transcripts giving rise to gradients of these proteins; this gradient defines the expression pattern for gap genes, which set up the boundaries between the different segments. The gradients produced from gap gene expression define the expression pattern for the pair-rule genes.
The pair-rule genes are transcription factors, expressed in regular stripes down the length of the embryo. These transcription factors regulate the expression of segment polarity genes, which define the polarity of each segment. Boundaries and identities of each segment are defined. Within the arthropods, the body wall, nervous system, kidneys and body cavity are segmented, as are the appendages; some of these elements are not segmented in the onychophora. While not as well studied as in Drosophila and zebrafish, segmentation in the leech has been described as “budding” segmentation. Early divisions within the leech embryo result in teloblast cells, which are stem cells that divide asymmetrically to create bandlets of blast cells. Furthermore, there are five different teloblast lineages, with one set for each side of the midline; the N and Q lineages contribute two blast cells for each segment, while the M, O, P lineages only contribute one cell per segment. The number of segments within the embryo is defined by the number of divisions and blast cells.
Segmentation appears to be regulated by the gene Hedgehog, suggesting its common evolutionary origin in the ancestor of arthropods and annelids. Within the annelids, as with the arthropods, the body wall, nervous system, kidneys and body cavity are segmented. However, this is not true for all of the traits all of the time: many lack segmentation in the body wall and musculature. Although not as well studied as Drosophila, segmentation in zebrafish and mouse is studied. Segmentation in chordates is characterized as the formation of a pair of somites on either side of the midline; this is referred to as somitogenesis. In chordates, segmentation is coordinated by the wavefront model; the "clock" refers to the periodic oscillation of specific genes, such as Her1, a hairy/Enhancer of split- gene. Expression starts at moves towards the anterior; the wavefront is where the somites mature, defined by a gradient of FGF with somites forming at the low end of this gradient. In higher vertebrates including mouse and chick, but not zebrafish, the wavefront depends upon retinoic acid generated just anterior to the caudal FGF8 domain which limits the anterior spreading of FGF8.
Cells at this point will form a pair of somites. Elaboration of this process with other signalling chemicals allows for structures such as muscles to span the basic segments. Lower vertebrates such as zebrafish do not require retinoic acid repression of caudal Fgf8 for somitogenesis due to differences in gastrulation and neuromesodermal progenitor function compared to higher vertebrates. In other taxa, there is some evidence of segmentation in some organs, but this segmentation is not pervasive to the full list of organs mentioned above for arthropods and annelids. One might think of the serially repeated units in many Cycloneuralia, or the segmented body armature of the chitons. Segmentation can be seen as originating in two ways. To caricature, the'amplification' pathway would involve a single-segment ancestral organism becoming segmented by repeating itself; this seems implausible, the'parcellization' framework is preferred – where exis
Lamella (surface anatomy)
In surface anatomy, a lamella is a thin plate-like structure one amongst many lamellae close to one another, with open space between. Aside from respiratory organs, they appear in other biological roles including filter feeding and the traction surfaces of geckos. In fish gills there are two types of lamellae and secondary; the primary gill lamellae come out of the interbranchial septum at the fish gill filament to increase the contact area between the water and the blood capillaries that lie in the fish gill filaments. The secondary gill lamellae are small lamellae that come out of the primary ones and are used to further increase the contact area. Both types of lamellae are used to increase the amount of oxygen intake of the blood. Both types of lamellae contain huge amounts of capillaries and are the sites where the exchange of oxygen from the water and carbon dioxide from the blood occurs. Pecten – the similar structure in birds
Coenagrion is a genus of damselflies in the family Coenagrionidae called the Eurasian Bluets. Species of Coenagrion are medium-sized, brightly coloured damselflies; the genus Coenagrion includes the following species
The insect family Coenagrionidae is placed in the order Odonata and the suborder Zygoptera. The Zygoptera are the damselflies, which although less known than the dragonflies, are no less common. More than 1,100 species are in this family; the family Coenagrionidae has six subfamilies: Agriocnemidinae, Coenagrioninae, Ischnurinae and Pseudagrioninae. This family is referred to the pond damselflies; the Coenagrionidae enjoy a worldwide distribution, are among the most common of damselfly families. This family has the smallest of damselfly species. More than 90 genera of the family Coenagrionidae are accepted; the name may be derived from common and agrio meaning fields or wild. Have a black pattern Ground color may be green, yellow, orange, or purple Narrow, stalked colorless and clear wings Two antenodal cross veins Vein M3 arising nearer to nodus than arculusAdults are seen around various habitats including ponds and wetlands; the females lay their eggs among living or dead submerged vegetation, in some species crawl about underwater depositing their eggs.
The nymphs are found in debris or among living or dead submerged plant material. The following is a complete list of genera: List of damselflies of the world Info and Photos at BugGuide Images from Georgia, US
The variable damselfly or variable bluet is a European damselfly. Despite its name, it is not the only blue damselfly prone to variable patterning, its behaviour is much like that of the azure damselfly. Immatures are found in adjacent meadows or uncut grassy areas; the male variable damselfly has a distinctive "wine glass" marking on the second segment of the abdomen. This is a black U-shaped mark with a black line joining the segment's narrow terminal black band. Male forms Female forms The variable damselfly occurs throughout Europe. Scattered and uncommon in mainland Britain but widespread and common in Ireland. Http://www.brocross.com/dfly/species/pulch.htm
In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. Some definitions limit the term to pairing between animals, while other definitions extend the term to mating in plants and fungi. Fertilization is the fusion of both sex gamete. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization. Mating may lead to external fertilization, as seen in amphibians and plants. For the majority of species, mating is between two individuals of opposite sexes. However, for some hermaphroditic species, copulation is not required because the parent organism is capable of self-fertilization; the term mating is applied to related processes in bacteria and viruses. Mating in these cases involves the pairing of individuals, accompanied by the pairing of their homologous chromosomes and exchange of genomic information leading to formation of recombinant progeny. For animals, mating strategies include random mating, disassortative mating, assortative mating, or a mating pool.
In some birds, it includes behaviors such as feeding offspring. The human practice of mating and artificially inseminating domesticated animals is part of animal husbandry. In some terrestrial arthropods, including insects representing basal phylogenetic clades, the male deposits spermatozoa on the substrate, sometimes stored within a special structure. Courtship involves inducing the female to take up the sperm package into her genital opening without actual copulation. In groups such as dragonflies and many spiders, males extrude sperm into secondary copulatory structures removed from their genital opening, which are used to inseminate the female. In advanced groups of insects, the male uses its aedeagus, a structure formed from the terminal segments of the abdomen, to deposit sperm directly into the female's reproductive tract. Other animals reproduce sexually including many basal vertebrates. Vertebrates reproduce with internal fertilization through cloacal copulation, while mammals copulate vaginally.
Like in animals, mating in other Eukaryotes, such as plants and fungi, denotes sexual conjugation. However, in vascular plants this is achieved without physical contact between mating individuals, in some cases, e.g. in fungi no distinguishable male or female organs exist. Yeasts are eukaryotic microorganisms classified in the kingdom Fungi, with 1,500 species described. In general, under high stress conditions like nutrient starvation, haploid cells will die. Protists are a large group of diverse eukaryotic microorganisms unicellular animals and plants, that do not form tissues. Eukaryotes emerged in evolution more than 1.5 billion years ago. The earliest eukaryotes were protists. Mating and sexual reproduction are widespread among extant eukaryotes including protists such as Paramecium and Chlamydomonas. In many eukaryotic species, mating is promoted by sex pheromones including the protist Blepharisma japonicum. Based on a phylogenetic analysis and Roger proposed that facultative sex was present in the common ancestor of all eukaryotes.
However, to many biologists it seemed unlikely until that mating and sex could be a primordial and fundamental characteristic of eukaryotes. A principal reason for this view was that mating and sex appeared to be lacking in certain pathogenic protists whose ancestors branched off early from the eukaryotic family tree. However, several of these protists are now known to be capable of, or to have had, the capability for meiosis and hence mating. To cite one example, the common intestinal parasite Giardia intestinalis was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex. However, G. intestinalis was found to have a core set of genes that function in meiosis and that are present among sexual eukaryotes. These results suggested that G. intestinalis is capable of meiosis and thus mating and sexual reproduction. Furthermore, direct evidence for meiotic recombination, indicative of mating and sexual reproduction, was found in G. intestinalis. Other protists for which evidence of mating and sexual reproduction has been described are parasitic protozoa of the genus Leishmania, Trichomonas vaginalis, acanthamoeba.
Protists reproduce asexually under favorable environmental conditions, but tend to reproduce sexually under stressful conditions, such as starvation or heat shock. Animal husbandry Breeding in the wild Breeding season Evolution of sex Lordosis behavior Mate choice copying Mating system Reproduction Sex determination system Sexual conflict Sexual intercourse Introduction to Animal Reproduction Advantages of Sexual Reproduction