202 POLYDORA OILIATA. 



tapered a little anteriorly and more gradually posteriorly, where it ends in a cup-like 

 process with a dorsal notch. The segments vary from sixty to seventy-one or more. 

 Colour in life yellowish-brown or straw-yellow, with the broad, red median dorsal vessel 

 as a conspicuous band. Some have the tentacles marked with dark pigment-bars, and 

 dark pigment often occurs on the snout. Numerous thecate Infusoria occur along the 

 body at the bases of the bristles. 



The first foot has a flattened, though rather long and narrow, bluntly-conical dorsal 

 lamella apparently without bristles. The ventral division has a setigerous process and a 

 group of bristles with tapered tips and traces of wings, their direction being slightly 

 backward. 



The next three segments have increasingly distinct dorsal and ventral divisions. 

 The dorsal has a well-marked lamella of an elongate conical form, with a tuft of long 

 bristles in front of it arranged in the typical manner, the longest being superior, and 

 all are curved backward. The shorter lower forms have the wings most distinct. All 

 likewise have a backward curve. The ventral division has a short conical lamella or 

 process, in front of which the shorter bristles project. These have very distinct wings, 

 thus increasing the breadth of the tip in certain views. 



The fifth bristled segment is indicated by an apparent constriction of the body -wall, 

 a feature due to the absence of lamellas and the long simple bristles. It bears the large and 

 characteristic strong hook-like bristles or crotchets (the abnormal bristles of Mesnil)^ besides 

 the dorsal and ventral series of simple tapering winged bristles. The fully developed hooked 

 bristle has a broad base, increases in diameter as far as the middle, and then diminishes 

 to the bend of the hook at the tip (Plate CVI, figs. 2 b and 2 c). At the bend is a lateral 

 spur, which sometimes escapes observation, and the organ tapers to a point which is more 

 or less acute according to its condition as regards wear. The posterior and developing 

 forms have a much more acute tip. About five have their points projecting beyond the 

 surface, the concavity of the distal curve being directed posteriorly. 



The sixth segment has the conical dorsal lamella, longer dorsal bristles, and ventral 

 series of bristles similar to those in front of the fifth, though in an example at St. 

 Andrews an imperfect set of hooks, that is, with the tips indistinct, occur ventrally, 

 whilst the seventh has in addition the first branchia at the inner edge of the dorsal 

 lamella (Plate LXXXVIII, fig. 4), and the ventral division bears winged hooks (Plate CVII, 

 fig. 2 d), and these are continued to the posterior end. 



The branchiae begin on the seventh bristled segment as fairly large strap-shaped 

 organs, increase in size to the nineteenth, and then diminish to the twenty-second, which 

 is attached to the twenty-eighth foot in the example under examination, but in others they 

 reach thirty-one in number. Mesnil remarks that only the last ten segments are devoid 

 of vestiges of these organs. This quite differs from the condition in the British examples. 

 The branchia is a strap-shaped structure with a vascular loop in its centre, and a dense 

 line of long cilia along the inner and anterior surfaces. They slightly taper toward the 

 tip, which is bluntly rounded. Bands of cilia occur on the dorsum between the feet. 



Immediately behind the branchial region the segments become somewhat wider, 

 then again become narrower, with prominent setigerous processes. The dorsal bristles 

 do not show any marked divergence in length throughout their course, though the first 



