POLYMNIA NEBULOSA. 133 



present a median process laterally in front of the point of contact of the hook-row. They 

 are usually fourteen or fifteen in number, the anterior narrow shields being ridged 

 (two-ringed), the posterior flattened. Occasionally an abnormality occurs in the 

 arrangement of the two rings anteriorly, the broad posterior ring ceasing like a fold 

 in the middle line. Reproduction of the tail is common. 



The mucous glands form a dense series of orange tufts in the thoracic region on 

 each side of the middle line and extend forward to the anterior end. They are long 

 and much folded and frilled anteriorly, and the contents tinge the long anterior ones 

 white with the exception of the orange tips. The contents consist of granular cells, 

 granules and protoplasmic threads and vesicles. In the small forms from the Channel 

 Islands the five posterior ventral shields in well-preserved examples present a symmetrical 

 arrangement, each being broadly fan-shaped in front, constricted posteriorly, and sending 

 out a spur on each side in front of the succeeding shield. 



The Hebridean forms are orange-red, sometimes inclining to brown, speckled all 

 over (tentacles, body and branchiae) with white (on tubercles, Daly ell), and the larger 

 examples are darker than the smaller. The oral region is purplish- red, also spotted with 

 white. Those from the Channel Islands are paler than the foregoing, but also speckled 

 with white on. both body and branchiae. The tentacles in the latter are irregularly barred 

 with white, and in young specimens from Herm they are milk-white. The specks rapidly 

 disappear in spirit. 



The branchiae are three in number on each side, and have a dull red colour spotted 

 with white. The first pair are about 1 inch long in large specimens, and arise from the 

 second body-segment, which has a spout-like fold at each side. The main stem is often 

 unbranched for some distance, whilst in others (large) a small branch or two occur 

 close to the base. The whole organ is sub-dichotomously divided, the short terminal 

 divisions giving a character to the mass which appears to form a dense arbuscle. In 

 many of the divisions the branches spring from one side only, but this does not appear 

 to hold in the distal divisions. The ring at the base of the first branchia trends evenly 

 away from it to the frill near the external margin of the mouth. A small papilla 

 sometimes occurs close to the base of the second branchia — it may be only on one side — 

 whilst ventralward the anterior fillet of the segment has a free process like a flat papilla. 

 Close to the outer base of the third branchia is the first setigerous papilla, and a 

 short distance ventralward is a similar free flattened process to that described in the 

 previous segment. 



In young examples the branchiae are comparatively simple, though the terminal 

 divisions correspond in general structure with that of the adult, and in a small littoral 

 variety from St. Peter Port, Guernsey, the branchiae are likewise less bushy, though the 

 terminal branches are typical. 



The setigerous processes are seventeen in number, commencing, as indicated, at 

 the third branchia and continuing for sixteen segments thereafter. Each is a somewhat 

 flattened papilla with the bristles arranged in a vertical row in the centre. The first 

 tufts of bristles are smaller, the bristles themselves shorter, but they show two groups, 

 as in the posterior, viz., a shorter series in this case without evident wings, and a longer 

 series also without evident wings, and with slightly curved and tapered tips. In the 



