268 THE ANNELIDA POLYCHAETA. 



Branchiae first appear on the sixth parapodia and continue to be strongly- 

 developed on all subsequent parapodia to the end of the fragment (somite 

 CLXXXII). The first and second branchiae are unifilamentous, each filament 

 slender, tapered, and nearly equalling the notocirrus in length. The third to 

 seventh branchiae, inclusive, are bifilamentous, the branch arising proximad of 

 the middle and projecting forward at an angle of about forty-five degrees from 

 the principal filament. (Plate 41, fig. 8). The eighth branchiae on the left side 

 is trifilamentous, a second branch springing from the caudal side between the 

 base and the first branch at a similar angle, while the right branchia is bifila- 

 mentous. The ninth branchia on the left side, on the contrary, is bifilamentous, 

 while that of the right side is trifilamentous. (Plate 41, fig. 9). Subsequent 

 branchiae acquire four and then five or sometimes six filaments, these in the 

 middle region of the body being, like the notocirri, long and surpassing the 

 middorsal line, while their arrangement is prevailingly unilaterally pectinate. 

 (Plate 41, fig. 10). Five filaments is the number maintained almost exclusively 

 in the branchiae excepting in the most anterior ones and some irregularities in 

 the most posterior, which are also shorter. 



The so-called dorsal acicula consist of a fascia of slender setae or fibers 

 extending into the base of the notocirrus. The ventral acicula are arranged in 

 a series, often of four. They are dark brown in color, and stout, distally finely 

 pointed, the colorless tip projecting freely from the surface. (Plate 40, fig. 6). 

 On each of the first five pairs of parapodia there occurs a series of stout compound 

 crochets in which the joint is distinct. Each is distally tridentate, the apical 

 tooth much larger, suberect, but curving distally outward beyond the others, 

 which are short and project nearly at right angles to the axis. The membran- 

 ous sheaths rise well above the apex, but are not prolonged into a slender tip. 

 (Plate 41, fig. 7). In addition these anterior parapodia bear a small dorsal 

 group of Umbate setae. These are short and very finely tipped, expanding near 

 the middle of the exposed portion, where they are narrowly limbate, and again 

 a little narrower proximad of this. On the sixth parapodia the compound 

 crochets are replaced by stout simple setae, which are distally attenuated to a 

 very fine tip. Farther caudad the true crochets make their appearance, these 

 normally two, but sometimes three, in number in each parapodium. These are 

 dark in color. The exposed portion of each is narrowed distad to a neck-like 

 constriction below the teeth, which are two in number. The lower tooth is 

 much the larger and is nearly transverse. The upper one, vertical proximally, 

 is abruptly curved distally. The membranous guards scarcely exceed the teeth, 



