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Show 976 MR. W. M. THOMSON ON A BRANCHIATE [Dec. 18, Here and there along the sides of the body the tips of the dorsal cirri may be seen protruding. The tips of the stout neuropodial bristles are also visible at certain points (Plate L X . fig. 1, ch.). W h e n the body is viewed from below, the eye is at once caught by the stout parapodia (Plate L X . fig. 2) and by the large mouth. The body consists of 27 segments, including the peristomium and the pygidium, which do not carry typical parapodia ; of which, therefore, there are only 25 pairs. Each parapodium is provided with a ventral cirrus, and just at the point of attachment of the foot with the body there occurs a prominent nephridial papilla (Plate L X . fig. 2, neph.) These become less marked towards the anterior end, and are absent from the first four or five pairs of parapodia' (the rudiments show up more clearly in some specimens than in others). Each papilla springs from the body, from the corner of a little square area raised into ridges, these areas forming a band down each side of the body. The middle of the body is occupied by a smooth surface, marked with fine transverse lines. Down the median line is a reddish-brown line seen, by transparency, lying in the mid-ventral groove, and representing the ventral nerve-cord. The colour is probably due to haemoglobin, which has been demonstrated by Prof. Bay Lankester [1] in the nerve-cords of Aphrodita aculeata. The mouth is very conspicuous and is bounded by four large thick lips, of which one is posterior and transverse, two are lateral and obliquely placed, while the fourth, median anterior, is wedged in between the oblique lips. The actual position of the mouth seems to be between the second and third pairs of parapodia ; in other words, the mouth has moved backwards from its primary position, so that three segments with their appendages lie in front of the mouth, a phenomenon which we are accustomed to meet with in Arthropods2. The mouth is thus further back than is represented in most of the figures of Lepidonotus available. The median anterior lip hides the base of the median tentacle and is separated from it by a deep groove, so that it cannot be mistaken for a facial tubercle. Beturning to tbe dorsal surface (Plate L X . fig. 3),after the removal of the elytra it is seen that the upper surfaces of the parapodia are produced towards the centre of the back as broad, flat ridges, of which the usual alternate ones carry the elytra. These ridges are oblong or rectangular in shape, with distinct edges, and are separated by 1 The absence of nephridial papillae from the more anterior segments in Polynoids was remarked by Bourne [3] for L. clavus, in which papillae are stated to be absent from the first 8 segments, as is also tbe case in several species recorded recently by H . Johnstone [9]. 2 This shifting of the mouth in Annelids back through one or more segments occurs in Amphinornidse, Accetidse, in Chrysopetalum, and in Aphrodita ; but it has been but little remarked upon in connection with the same phenomenon, to which Lankester was the first to draw attention, in the case of Arthropoda. Its occurrence in these families of Annelids, all of which are undoubtedly much modified as compared with the typical annelid, is of interest and of theoretical importance.-W. B. B. |