THE ANATOMY OF SOALIBEEGMA INFLATUM. 243 



Behind the swollen portion the body tapers gradually to the 

 posterior end. 



The animal is strongly convex above but flattened below. 

 There is a depressed area along- almost the whole length of 

 the mid-ventral line (marking the position of the nerve-cord), 

 which is divided by transverse grooves into a series of 

 squarish or hexagonal areas (fig. 2). In some specimens the 

 position of the oesophageal connectives is also marked ex- 

 ternally by two shallow depressions, the metastomial grooves, 

 which pass round the mouth and unite at the anterior end of 

 the mid-ventral groove. 



The head or prostomium is distinct and well developed, 

 forming a somewhat quadrangular mass overhanging the 

 mouth, and bearing at each side anteriorly a short rounded 

 tentacular process (fig. 3). 



Immediately behind the head there is an achjetous peri- 

 stomial segment, composed of two annuli. The rest of the 

 body of the animal is divided into segments bearing para- 

 podia. Each of the first three cha^tigerous segments is 

 composed of three annuli, the middle annulus bearing a 

 prominent pad on each side, from Avhich the neuropodium 

 and the notopodium arise. All the following fully-formed 

 segments of the body are divided into four annuli, on the 

 third of which the parapodia are borne (figs. 1, 2). In the 

 large specimen, 56 mm. long (fig. 1), sixty-one segments (in 

 addition to the peristomium and pygidium) may be dis- 

 tinguished. The parapodia are clearly visible on all the seg- 

 ments up to and including the fifty-thiid ; those of the next 

 four segments are very small, the dorsal cirrus being the only 

 easily visible appendage. The last four segments of the 

 animal are divided from one another only by faint grooves, 

 and do not bear parapodia. Following these there is a very 

 short terminal portion or pygidium, which even in large 

 specimens is only about "3 mm. long. There are four pairs 

 of branched shrubby gills, situated immediately behind the 

 notopodia of the second, third, fourth, and fifth cliEetigerous 

 segments (for further description of the gills see p. 262). 



