Chaetopterus Variopedatus. 485 



their length is half the width of the plastron and the diameter of 

 the base half the length of each appendage. Together with the broad 

 plastron they either form a plane, or the whole may be directed dor- 

 salward at the margin so that a cross section would be crescentic in 

 outline. The integument of the dorsal side of the appendages is 

 more transparent than in any other portion of the anterior region 

 and the seta? with their protractor muscles may be seen through its 

 transparent walls. 1'he setae are arranged in the form of a fan. 

 Their lanceolate ends protrude in a line along the ventral side of each 

 of these rami and are directed laterally along the rami. The ventral 

 setae of the fourth setigerous segment are black and somewhat club- 

 shaped at their external ends. Their shafts are thick and bear 

 annulations which are not detected in the slender shafts of the lan- 

 ceolate seta?. The number of setse varies with the age of the indi- 

 vidual. I have found as few as five in each parapodium in a young 

 individual to ninety in an adult specimen of average size. 



The first pair of setigerous appendages is located just beneath the 

 dorsally-directed ends of the ventral lip of the mouth. It is con- 

 siderably smaller than the other parapodia, which increase progres- 

 sively to the ninth pair. These conical appendages are regarded by 

 Jourdain as the dorsal rami of the parapodia, and the somewhat 

 triangular epaulet-like appendages of the ninth pair he regards as the 

 ventral rami of the parapodia. 



The ventral surface of the anterior region consists largely of a 

 yellowish to a reddish yellow granular area surrounded by a narrow 

 border of lighter color. It extends around the whole ventral surface 

 of the anterior region encircling the ventral lip and extending between 

 the rows of dorsal rami on each side and the yellowish '^plastron" 

 just described. In section the plastron consists of long columnar 

 cells of ectoderm (Figs. 15, 16). 



The dorsal surface of the anterior region bears a ciliated groove 

 (Figs. 5, 15-18) which extends in a middorsal line from a point just 

 behind the thickened rim of the dorsal lip of the buccal funnel, to 

 the middle of the first segment (twelfth of the whole animal) of 

 the middle region. At this point it diverges to the right and to the 

 left along the large aliform appendages. It functions as an important 

 accessory feeding organ, as I shall show. 



