586 ORGANS OF SECRETION. 



observe several distinct salivary follicles in the trombidium, 

 and other genera, and two in the scorpion ; the liver consists 

 generally of clusters of small follicles, which, in the scorpion, 

 open into the stomach by five pairs of short hepatic ducts ; 

 and the urinary tubuli of the spiders form a small bladder, 

 as in many insects, before sending their secretion into the 

 cloacal part of the alimentary canal. The generative organs 

 of both sexes still present the tubular character of elongated 

 follicles, and poison-glands with poison-instruments are 

 developed in these animals, sometimes at the anterior and 

 sometimes at the posterior end of the body. In the scor- 

 pion, as in many insects, the last segment of the trunk is 

 converted into a sharp, piercing poison-sting, which is here 

 external, curved, solid at the point like the fang of a serpent, 

 grooved at each side, and provided with two lateral canals 

 continued from these grooves to the two poison-glands, 

 which are situate above the broad dilated bulbous base of 

 this exposed terminal sting. In the tarantulee and spiders, 

 as in the scolopendree, among the myriapods, the poison- 

 glands are situate at the sides of the mouth, and pour their 

 secretions through the perforated, sharp, curved, maxillse. 

 There are four small follicular glands in the lower and back 

 part of the abdomen in the spiders, which secrete the fine 

 glutinous threads that compose the webs, and send their 

 secretion through four ventral papillae, in front of the anus, 

 which are perforated with numerous very minute orifices, like 

 the nipples of many mammalia. These filamentous glands can 

 be suddenly compressed by the spiders, so as to throw out 

 the threads to some distance when required. 



Most of the numerous glands developed in insects and 

 other air-breathing articulata, are incompatible with the 

 aquatic life of the Crustacea, which have fewer secreting 

 organs than any other entomoid class. From the limited 

 circulation of the blood in myriapods, insects and arachnida, 

 their glands have generally a simple, isolated, elongated, 

 tubular form, adapted to reach the fluids of the body ; but 

 in the aquatic forms of Crustacea and annelides, where fewer 

 glands are required, and where the sanguiferous system is 

 more extensively distributed through the tissues for their 

 nutrition, the secreting organs have a more subdivided, 

 ramified, or conglomerate character, as the blood can be here 



