. A manual of zoology. Zoology. 300 ARTHROrODA enlarged into a slcravjl pofkti, just in front of wliich the excretory tubules empty. These resemlile tire Malpigliian tubes of insects in function, but differ in being entodermal in origin. Besides tliere are also coxal glanils (modified nephriiha), of \vluch only one pair comes to development, and tliis may lose its external opening on the base of fJie lirst or third leg. The cxsophagus is always closely surrounded by a nerve ring composed of brain abo\'e and of part of tire ventral chain on the sides and below, the thoracic and more or fewer of
. A manual of zoology. Zoology. 300 ARTHROrODA enlarged into a slcravjl pofkti, just in front of wliich the excretory tubules empty. These resemlile tire Malpigliian tubes of insects in function, but differ in being entodermal in origin. Besides tliere are also coxal glanils (modified nephriiha), of \vluch only one pair comes to development, and tliis may lose its external opening on the base of fJie lirst or third leg. The cxsophagus is always closely surrounded by a nerve ring composed of brain abo\'e and of part of tire ventral chain on the sides and below, the thoracic and more or fewer of the abdominal ganglia entering into its composition (tig. 370, D). Of sense organs, besides tactile hairs, only tire eyes (fig. 37r), 2-12 in , are well known. The large number of rods in tire retina makes it probaftle that these eyes see well. Hearing is well developed, but it is uncertain whether certain hairs oir the legs and palpi are the auditory organs. The function of the lyriform organs, wliich occur in the sldn of body and legs in several groups, is unknown. The respiratory organs already alluded to (p. 3SS) have their spiracles, always few in itumber, on the anterior ventral part of the abdomen and, it is stated, sometimes on the cephalotliorax. The internal organs are the lungs and the trachea-. A lung is a rounded sac just inside tlie spiracle and consists of numerous lea\"es on the anterior wall of the lung sac. Each leaf contains a blood space in its interior, wliile between the leaves are tlat- tened spaces into wliich the air enters (fig. 41(1). The trache;r are branched tubes arising front the abdominal spiracles and penetrating the abdomen (fig. 4-o)- These are Uned with cliitin, and to Ty^'-y^^S^ strengthen them without undue tliickness tliis lining is thrown into folds, usually arranged in a spiral. In the scorpions and tetrapneumonous Araneina only lungs occur. In other spiders one pair of lungs is replaced by trachea-, wliile in most other ar
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
