1904.] NATURAL SCIENCES OF PHILADELPHIA. 485 



The fii-st distinct parapodium is on the somite following the peris- 

 tomium and consists of a setigerous body with three cirri, a postsetal 

 lobe and a dorsal and ventral cirrus, all slender and conical and the latter 

 about tT\-ice as long as the others. The second and third parapodia are 

 similar, with the dorsal cirri longer. As far as the sixth or seventh the 

 dorsal cirri continue to increase in length, then gradually diminish 

 through the branchial region, and behind the latter remain small and 

 slender to the end. The ventral cirrus undergoes no change in the first 

 four parapodia, but suddenly disappears in the fifth, where it is repre- 

 sented by a small glandular prominence, which increases in size and in 

 the middle branchial region extends about one-fourth of the distance 

 across the venter. Beyond the branchial region it becomes smaller. 

 The postsetal lobe is likewise largest on the first four somites, and after 

 reduction in the first few branchial segments, accompanied by a rota- 

 tion ventrad, remains for the entire middle region of the body a blunt, 

 moderately sized lobe ventro-caudad of the setse tuft. In the posterior 

 half of the body all parts of the parapodia are reduced and finally 

 become mere low papillae. 



In the region of their greatest development the branchiae are large 

 and prominent, of a tall and slender form, much like a juniper tree, but 

 with the spirally disposed branches more open in arrangement and, 

 below them a distinctly annulated basal portion of the trunk. They 

 begin abruptly on the fourth parapodium, and the first is about 

 three-fifths as long as the largest on the sixth or seventh parapodium. 

 Beyond this point they gradually decrease in size, the number of 

 whorls of branches at the same time increasing, and their arrangement 

 becoming more open. By the twenty-seventh parapodium the spiral 

 arrangement has disappeared altogether and the stem is simply curved, 

 with the branches in a linear series on the convex side, an arrangement 

 which begins to appear at the tip of some of the preceding gills, as 

 though they were gradually unwinding. The number of turns in 

 different branchiae of the type is 11 on the first, 13 on the second, 

 15 on the third and foiu-th, 13 on the sixth, 10 on the tenth, 7 on the fif- 

 teenth, 4 on the twentieth, and none on the twenty-fifth. Beyond 

 the thirtieth parapodium each gill consists merely of a stalk, usually 

 curved at the free end and bearing a terminal tuft of short branches, 

 with a few others in a series below. These gradually decrease in size, 

 and by the fortieth parapodium are nearly or quite simple, and finally 

 disappear by the sixtieth parapodium. 



On the first four parapodia the setae are of two kinds, guarded uncini 

 and simple slender setae. The former are nearly colorless and have ' 



