192 POLYCIRRUS MEDUSA. 



extent supplant them. From the nature of the parts no prominent ventral lip is present, 

 but the narrow part of the first glandular ventral scute glides under the ventral flaps of 

 the cephalic plate and runs into the smooth surface, which trends as a shallow groove 

 forward to the mouth. 



The body reaches 2 to 4 inches in length, is more or less dilated anteriorly, 

 sometimes being largely distended, and it tapers posteriorly to the tail, which in the 

 preparations is by no means slender, though in life it is often much more attenuate. 

 It is rounded dorsally, grooved ventrally, and has numerous segments, fifty to eighty-eight 

 or more. Posteriorly it terminates in a crenate anus, the central papilla ventrally being 

 the most prominent. Occasionally the anus is carried outward on a small process or 

 appendix, but such may be due to regeneration. Anteriorly are thirteen pairs of 

 setigerous processes, and behind these about seventy or more uncinigerous processes 

 which occupy the ventro-lateral region. 



The muscular fibres of the intestine are curiously reticulated, spaces being left 

 between the fibres, and apparently there are no evident circular fibres, though the oblique 

 and connecting fibres would suffice for constriction. 



The segment behind the mouth has a single large granular ventral scute, narrow 

 in front and broad and rounded posteriorly. Then a narrow belt follows, its lateral 

 regions expanding to include the second setigerous processes. Thereafter a median band 

 with a central line passes longitudinally backward, cutting the scutes into pairs in each 

 segment, and of these seven or eight are distinct, each marked by transverse lines. The 

 segments of the posterior region have a deep furrow in the preparations dividing them 

 into two, and each of these is again subdivided into three narrow rings. 



Viewed from the dorsum each setigerous process is dorsally bifid— a feature better 

 marked in the smaller than in the larger examples, and the bristles issue between the 

 limbs. The first setigerous process has a considerably longer anterior cirrus than those 

 which follow, the posterior process being smaller. In the middle of the body the 

 anterior process is shorter and thicker, and the posterior process is more distinct, whilst 

 the last setigerous process in some has a rounded boss on the tip of the thick, short, 

 anterior process, and the posterior is at a greater distance from it and smaller 

 than in the middle of the series. From this bifid region the tip is curved downward 

 and inward. 



The bristles (Plate CXXVI, figs. 9 and 9 a) are in two groups, a longer and a shorter 

 series. The former are pale golden slender bristles with shafts more attenuate than their 

 pale bases, and which taper distally to the curved, almost wingless tip. In the shorter 

 series only the curved tips, which are more slender than the foregoing, project beyond the 

 surface. The margin from which the bristles issue slopes inward as it passes ventrally, 

 and the fascicle has a twist as in Streblosoma. 



The first uncinigerous process occurs as a slightly elevated ridge at the posterior 

 part of the segment following the last bristle-bundle, and the succeeding processes 

 gradually increase in prominence until they form bosses or papillas like the "feet" of 

 caterpillars along the ventro-lateral region of the body to the tail, the terminal processes 

 being small and closely arranged. The single row of hooks lies on the anterior face of the 

 tip. The anterior hooks (Plate CXXVI, fig. 9 b) have a base considerably longer than 



