. The biology of spiders. Spiders; Insects. GENERAL CHARACTERISTICS 3 both by their coelomic cavities and by two nerve-masses or neuromeres. Appendages do not exist on the first somite, though it is possible that they are represented by the eyes. The chelicerae are the appendages of the second somite. The five conspicuous limbs which follow, namely, the palps and the four pairs of legs, indicate a coalescence of five further somites, the result being the construction of a cephalothorax, a head or cephalon and breast or thorax fused together. The reason for being patient with technical ter
. The biology of spiders. Spiders; Insects. GENERAL CHARACTERISTICS 3 both by their coelomic cavities and by two nerve-masses or neuromeres. Appendages do not exist on the first somite, though it is possible that they are represented by the eyes. The chelicerae are the appendages of the second somite. The five conspicuous limbs which follow, namely, the palps and the four pairs of legs, indicate a coalescence of five further somites, the result being the construction of a cephalothorax, a head or cephalon and breast or thorax fused together. The reason for being patient with technical terms like " prosthomeres " is that they are less misleading Fig. i.—Diagram of Embryo Arachnid Head. In embryo, somite ii is not yet in front of mouth. From Lankester. E, eye ; CH, chelicerae ; M, mouth ; i-iv, coelom of somites, 1-4. than easy-going popular words like " head " and even " thorax," which are too suggestive of man or mammal. The region behind the cephalothorax, the opisthosoma, generally called the abdomen, is composed of twelve seg- ments or somites. The first of these is the so-called pre- genital segment of scorpions and is represented by the " waist " of the spider. The second and third somites of at least some of the terrestrial forms bear the lung-books. The fourth and fifth somites are of interest because in spiders they retain their appendages in the form of spinnerets, of which primitively there are eight, four (two endopodites and two exopodites) to each segment. The last seven somites are devoid of appendages in all living forms. The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Savory, Theodore Horace, 1896-. London : Sidgwick & Jackson
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecti, booksubjectspiders
