BY J AS. P. HILL. 



sacs are also concealed from view. The gonads in sexually 

 mature animals are found in the wings almost immediately behind 

 the posterior rim of the collar, and they extend in the ridges far 

 into the hepatic region. In sexually mature individuals the gonads 

 may distend the genital wings to such a degree that they stand 

 out almost horizontally to the body (fig. 23, giv.) and leave the 

 gill area exposed, but the usual condition is the one first descril)ed 

 where the gill area is completely concealed. 



The gill area may reach a length of 15 mm., and is thus 

 relatively very short. It is broadest just behind the collar, and 

 narrows slightly posteriorly; laterally it is bounded by two longi- 

 tudinal grooves which become gradually shallower posteriorly and 

 terminate at the end of the gill area. Into these the gill pores 

 open. 



(2) Hepatic Region: varies in length according to the 

 size and age of the animal. In one of my largest preserved 

 specimens it measured over 20 mm. in length with about 50 liver 

 sacs on each side. The number of sacs averages between 40 and 

 50 on each side, but there ma}^ be as many as 60. In fully 

 extended animals the liver sacs present a distinctly paired 

 arrangement in two longitudinal rows. They begin as small 

 elevations in contact with each other, and covered by the genital 

 wings; posteriorly they gradually' increase in size, and attain 

 their maximum development just beyond the point where the 

 genital wings are reduced to ridges. Behind this the sacs 

 gradually decrease in size to the posterior end of the region, 

 finally l^eing represented by two rows of small tubercles which 

 become gradually reduced until they disappear altogether. Each 

 «ac arises by a narrow^ base which widens out into an antero- 

 posteriorly compressed end, which in the region of the larger sacs 

 overhangs the reduced genital wings. The form of the sac in this 

 region is shown in fig. 24, hep. 



Variation in Hepatic Region. The sacs are 

 usually in close contact with each other by their anterior and 

 posterior faces, but occasionally some of the c?eca present the 



