ON A NEW ORGAN IN THE LTCOTilDEA. 389 



dorsal ciliated organ (PI. XXXIV, figs. 1, 2, 5, o. limb ; PI. 

 XXXV, figs. ] 5, 17, 0. limb). Fig. 15 represents a transverse sec- 

 tion through the dorsal muscle of another specimen, taken rather 

 farther back in the segment than that in fig. 5, thus avoiding 

 the blood-vessel. The ciliated organ curls round the edge of 

 the muscle, and ascends on its inner side nearly as high as the 

 slight angle formed where this muscle leaves the body-wall. 

 It will be seen that the inner limb (fig. 1, and figs. 15, 

 17, i. limb) does not adhere closely to the muscle, but 

 to a fold of the septum which is bounded anteriorly by the 

 dorsal tegumentary vessel (figs, 1, 4, 15, 17). The septum, in 

 fact, is not attached to the inner face of the longitudinal 

 muscle, and its free edge bends forward at right angles 

 (fig. 4, fl. sept.), and proceeds upwards, leaving a space be- 

 tween itself and the muscle (figs. 1, 4, 5, 15, 17) ; it is on 

 the inner side of this flap, which faces slightly backwards, 

 that is situated the inner limb of the dorsal ciliated organ 

 (figs. 1, 4, 5, and figs. 15, 17, i. limb). The outer and dorsal 

 limb varies somewhat in its extension, sometimes reaching 

 quite near the median dorsal line, as I have already mentioned. 

 In this region blind prolongations of the coelom run up be- 

 tween the longitudinal muscles and the body- wall (figs. 1, 5, 7, 

 dors, coel.) ; they are separated from each other by connective- 

 tissue walls. Small blood-vessels (fig. 7, bl. ves.) and bundles 

 of circular muscle-fibres run along the coelomic spaces (fig. 7, 

 circ. m.). The end of the outer limb of the dorsal ciliated 

 organ (fig. 7, o. limb) extends up the largest of these spaces 

 (which is situated almost exactly in the middle of each seg- 

 ment), being continuous with the coelomic epithelium which 

 lines the space and covers its anterior side. A branch of the 

 tegumentary vessel follows it closely during its course. I first 

 expected that this dorsal tubular prolongation of the coelom 

 would, with the outer limb of the ciliated organ, lead to an 

 external aperture; but I have looked in vain for such a pore in 

 numerous sections — transverse, sagittal, and horizontal. Both 

 coelomic space and ciliated organ gradually dwindle away until 

 they disappear altogether some little way from the median 



