i84 ANNUL AT A, 



dorso-laterally and are beautifully branched delicate organs 

 of respiration. Through their thin walls the blood and 

 outside water interchange carbonic acid and oxygen. The 

 posterior part (3) consists of a great number (about 30) of 



Fig. III. — A Magnified Gill-Segment of Arenicola. 



(After AsHWORTH and Gamble.) 



Notopodial Setae. 

 Branches of Gills. 



Annulus. 



/ 



Nephridiopore. Torus Uncinatus 



(Neuropodium). 



compressed segments, on none of which are there any 

 appendages or gills. 



Inteeu- '^^^ body is covered by a fine but definite 



mentarv ^^ticle secreted by the simple underlying ecto- 

 derm in which there are unicellular glands. 

 If the animal be cut open down the median dorsal line 

 the whole internal anatomy is exposed, for Arenicola is a 

 coelomate animal and all the internal organs lie in contact 

 with the ccelom. 



The coelom is spacious, as in Polygordius^ but it is not 



completely divided up into compartments. The front part 



Coelom ^^ divided by three transverse septa^^ between the 



first, second, third and fourth segments, which 



* The first septum has a pair of hollow septal pockets which are muscular, and 

 probably assist in protrusion of the pharynx. 



