. Outlines of zoology. or aortaand lateral vessels; and thecirculation corresponds in general to that of the scorpion. In a few forms (Tetrapneumones) respiration is effected by four lung-books, in the large bird-catching My gale (Fig. 193). In the vast majority (Dipneumones) there are two lung-books, and tubular tracheae in addition. The 24 37° PHYLUM ARTHROPODA. Stigmata of the lung-books lie on the anterior ventral surfaceof the abdomen; the trachea open posteriorly near thespinnerets, or just behind the opening of the lung-books, orat both places. The spinnerets (4-6) lie just in fron
. Outlines of zoology. or aortaand lateral vessels; and thecirculation corresponds in general to that of the scorpion. In a few forms (Tetrapneumones) respiration is effected by four lung-books, in the large bird-catching My gale (Fig. 193). In the vast majority (Dipneumones) there are two lung-books, and tubular tracheae in addition. The 24 37° PHYLUM ARTHROPODA. Stigmata of the lung-books lie on the anterior ventral surfaceof the abdomen; the trachea open posteriorly near thespinnerets, or just behind the opening of the lung-books, orat both places. The spinnerets (4-6) lie just in front of the anus. Theyare movable and perforated by numerous (often manyhundred) tubes or spinning spools, each of which isconnected with a compressible gland secreting silk. Thereare various kinds of glands; both the amount and thenature of the secretion are under control. The spinneretsare transformed abdominal appendages (a new organ froman old—as is so often the case); and the glands are ectodermic Many spiders have at thebase of their spinnerets atransverse surface or cribrel-lum perforated by spinningtubes, and from this theycomb out a peculiar curledsilk with the help of a rowof stiff bristles or calamistrumon each posterior leg. The males are usuallysmaller and often morebrightly coloured than theirmates. From the pairedtestes, in the anterior partof the abdomen, two vasadeferentia pass to a com-mon aperture beside the openings of the the paired ovary two oviducts likewise arise and openinto a uterus, whose external aperture is surrounded in themature female by a complex genital armature or also in most females are the openings of two recep-tacula seminis, in which the sperms received from a male arestored, and from which they pass by a pair of internal ductsto the oviducts, there to fertilise the ova. The sperms ofthe male, after emission, may be stored up in the last jointof the palps. The ova are usually surrounded by
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
