402 ;<;noLoaY sect. 



the mouth situated at tho base. The anus is sometimes terminal 

 and posterior, sometimes anterior and dorsal. There is an exten- 

 sive e(elome filled with a corpusculated fluid, and not divided by 

 septa. The ventral nervc-eord is not made up of a series of 

 ganglia. There is, as a general rule, only a single pair of nephri- 

 dia. The sexes are separate ; the ovaries and testes simple masses 

 of cells ; the nephridia act as reproductive ducts. The larva is 

 a trochophore. 



1. Example of the Chk9,?,—Sipuncuhis michm. 



Greneral External Features. — Siimnndus occurs on sand at 

 moderate depths off the coast in most countries outside of the 

 tropics. It is an elongated worm of a cylindrical shape, somewhat 

 narrower towards one — the anterior — end. There is no trace of 

 division into segments. The anterior portion of the bod}^, to the 

 extent of about a sixth of the total length, is capable of being 

 involuted within the part behind. The surface of this anterior 

 part, which is termed the introvert (Fig. 386), differs in appearance 

 from that of the rest of the body in being covered more or less 

 closely with chitinous papilla-. The papillas of the posterior 

 portion of the introvert are shaped like the bowl of a spoon, 



with the concavity turned to- 

 wards the body-wall and the 

 tip directed backwards ; the}' 

 are so closely arranged as to 

 overlap one another like the 

 .shingles of the roof of a house : 

 further back they become longer 

 and narrower, mammilliform, 

 and more scattered. When the 

 introvert is fully evaginated, 

 there appears at its extremity 

 etbafi ^ horseshoe-shaped fold of the 

 ''X4 '^^'/^''it'i-* *^^uW^'j^^ ' integument, the tentacular fold 



WiW^^i^amm^ r ° 



'^'•^iJf^'fi;Ai'''yM^&0^^ same somewhat the appearance 



/,i'v,,,,i, /i7 Qf ^ circlet of tentacles. For 



Fin. ssii.-Anterior extremity of sipun- ^ little spacc immediately be- 



cnlusnudus. ",i/, ,m.,,. antcnor papil- , ■ t .t , . i r i i j.i 



lary region ; imtl. ,.a/). posterior papillary nmCl the tCUtaCUlar lOlCl the 

 region ;,.,Me„tacular fold, (After Ward.) ^^^^j.^^^ ^^ ^j^^ iutrOVert is free 



from papillae. The posterior 

 portion of the body is devoid of papillce, but is marked out by a 

 series of narrow impressed lines into a number of elongated four- 

 sided areas. 



