THE PERIPATIDEA. 536 



curious habit of throwing out a web of viscid filaments when 

 handled or otherwise irritated. 



The head is distinct, and is provided with a pair of many- 

 jointed antenna-like tentacula and two simple eyes. The 

 mouth, situated upon the under surface of the head, is sur- 

 rounded by a prominent lip, which incloses a pair of jaws, 

 each of which is terminated by two curved chitinous claws, 

 similar to those of the feet. On each side of the mouth, the 

 head supports a short obscurely -jointed " oral papilla," which 

 is somewhat like one of the feet, but is devoid of claws and 

 perforated at its extremity. The head is followed by an un- 

 segmented body produced laterally into paired appendages, 

 which vary in number from fourteen to more than thirty, ac- 

 cording to the species ; and each of these appendages is in- 

 distinctly articulated, the terminal joint being provided with 

 two small curved claws. 



The anus is terminal, and the genital aperture is situated 

 on a papilli^, a little distance in front of the anus, on the 

 neural or ventral face of the body. 



The alimentary canal commences by an ovoid muscular 

 pharynx. The oesophagus, continued from this, gradually 

 dilates into a wide and long stomach, from which a very short 

 intestine is continued to the anus, situated at the posterior 

 end of the body. There are no Malpighian ca3ca. Two very 

 large ramified tubular glands, which secrete the viscid matter 

 of which the web is composed, lie at the sides of the alimen- 

 tary canal, and open outward by the perforations of the oral 

 papillae. A vessel occupies the middle line of the dorsal 

 body-wall, and is probably a heart. 



The respiratory organs are the trachea3 discovered by Mr. 

 Moseley. The numerous pores, or stigmata, from which the 

 trachere take their origin, are scattered all over the surface 

 of the body, one row being median and ventral. Each stigma 

 is the outward termination of a short, wide tube, which, at 

 its opposite end, branches out into a pencil of fine tracheae, 

 which rarely divide, and are distributed in great abundance 

 to the viscera. They are very delicate tubes, wdiich often 

 take an undulating course, and are rarel}^ more than -^-^-q 

 of an inch in diameter. In optical section, their walls have 

 a finely-beaded appearance, as if from the presence of trans- 

 verse thickenings, though distinct transverse markings are 

 rarely to be seen. 



The nervous system, as Milne-Edwards discovered, con- 

 sists of two ganglia in the head, closely united above the 



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