246 THE ANNELIDA POLYCHAETA. 



much more slender than the basal and relatively long, being about two thirds 

 as long as the basal. In the middle region of the body the ventral cirri have 

 become much reduced both in length and diameter and the Isasal article in 

 particular has become relatively much smaller, each cirrus as a whole being a 

 narrowly conical process, a form maintained to the caudal end of the body. 



The branchiae begin on the parapodia of the seventh somite and exist on 

 all subsequent ones to the end of the body, though on the last two pairs they 

 are almost obliterated. The first branchia consists of a single filament which 

 is a little shorter than the notocirrus, from the base of which it arises. The 

 second branchia is bifurcate, two filaments arising from a short common stalk; 

 the filaments clearly exceed the notocirrus. The succeeding four branchiae 

 are similar, each consisting of two slender equal filaments increasing in length 

 caudad, the sixth branchia falling but little short of reaching the middorsal line. 

 From the sixth the branchiae decrease again in length and become much reduced 

 in the middle region where they do not reach halfway to the middorsal line, 

 and then again increase in size caudad. The seventh branchia consists of three 

 filaments, the extra one apparently formed by bifurcation of the more dorsal of 

 the two filaments in a gill such as the preceding one, the third filament arising 

 on the outside of the stalk at a level below the other two; the eighth, ninth, 

 tenth, and eleventh are similar to the seventh, and the twelfth to eighteenth, 

 inclusive, are again bifurcate. The following branchiae are again composed 

 of single filaments, their simple branchiae occurring on all parapodia of the 

 remaining and greater portion of the body excepting on seven or eight pairs 

 preceding the last six or seven pairs, on which they are bifilamentous, the last 

 ones being again simple. The last few branchiae are much reduced. (Plate 56, 

 fig. 5-10). 



The acicula proper are pale in color ; the acuminate tips are narrowly rounded 

 and project but moderately; those of each parapodium lying in rather close 

 contact. The crochets extend obliquely through the parapodium and emerge 

 close to the neurocirrus. They are easily broken off. They are rather stout 

 and present the usual double curve in their free portion. Each is tridentate; 

 there is a large conical subapical tooth at right angles to the axis and a much 

 smaller apical tooth curved forwards and bearing well distad on its caudal side 

 the minute third tooth or denticle. The membranous guard extends over the 

 subapical tooth and rises angularly well above the level of the apical tooth. 

 (Plate 51, fig. 11). The crochets begin on the twenty fifth somite or a somite 

 adjacent to it. The setae of the dorsal group are strictly capillary and non- 



