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Near the end of the nineteenth century the hypothesis was presented for the homology of book lungs in arachnids and book gills in the horseshoe crab. Early studies with the light microscope showed that book gill lamellae are formed by outgrowth and possibly some invagination infolding of hypodermis epithelium from the posterior surface of opisthosomal limb buds. Scorpion book lungs are formed near the bilateral sites of earlier limb buds. Hypodermal invaginations in the ventral opisthosoma result in spiracles and sac-like cavities atria. In early histological sections of embryo book lungs, widening of the atrial entrance of some lamellae air channels, air sacs, saccules was interpreted as an indication of invagination as hypothesized for book gill lamellae.
Book lung , form of respiratory organ found in certain air-breathing arachnid arthropods scorpions and some spiders. Each book lung consists of a series of thin plates that are highly vascular i. These plates extend into an internal pouch formed by the external skeleton that opens to the exterior by a small slit. This provides an extensive surface for the exchange of oxygen and carbon dioxide with the surrounding air. There are four pairs in scorpions and up to two in spiders.
They are located in the abdomen , just below the pedicel , and are composed of many fine leaves. Blood is passed over a large surface area to absorb oxygen. The openings of the book lungs branchial opercula are situated on the ventral surface of the abdomen and may be closed to prevent water loss. Book lungs are believed to be the ancestral type of respiratory organ in arachnids. October 11, Retrieved October 11, from Encyclopedia.
A book lung is a type of respiration organ used for atmospheric gas exchange and is found in arachnids , such as scorpions and spiders. Each of these organs is found inside a ventral abdominal cavity and connects with the surroundings through a small opening.
A book lung is a type of respiration organ used for atmospheric gas exchange that is found in many arachnids, such as scorpions and spiders. Each of these organs is found inside an open ventral abdominal, air-filled cavity atrium and connects with the surroundings through a small opening for the purpose of respiration. Book lungs are not related to the lungs of modern land-dwelling vertebrates. Their name describes their structure. Stacks of alternating air pockets and tissue filled with hemolymph the arthropod equivalent of blood give them an appearance similar to a "folded" book. The unfolded "pages" plates of the book lung are filled with hemolymph. The folds maximize the surface exposed to air , and thereby maximize the amount of gas exchanged with the environment.
Metrics details. The transmission electron microscope TEM is used for the first time to study the development of book gills in the horseshoe crab. Near the end of the nineteenth century the hypothesis was presented for homology and a common ancestry for horseshoe crab book gills and arachnid book lungs. The present developmental study and the author's recent ones of book gills SEM and scorpion book lungs TEM are intended to clarify early histological work and provide new ultrastructural details for further research and for hypotheses about evolutionary history and relationships. The observations herein are in agreement with earlier reports that the book gill lamellae are formed by proliferation and evagination of epithelial cells posterior to opisthosomal branchial appendages.
A quote from JBS Haldane, one of the founders of the evolutionary synthesis, illustrates the taxonomic concentration of biodiversity. When asked about what he could divine from nature about the Creator, Haldane replied that he must have had " an inordinate fondness for beetles. They are Ecdysozoans , have a cuticular skeleton and hence must molt to grow. The most successful phylum they are considered most closely related is the Nematoda. Like nematodes, they shed their outer covering as they grow, but the arthropod cuticle differs both in structure and function from that of nematodes. They posses hard segmented exoskeletons. One of the interesting true morphological synapomorphies is the complete loss of motile cilia in adult and larvae stages.