976 MB. W. M. THOMSON ON A BEANCHIATH [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 LX. fig. 1, ch.). 



When the body is viewed from below, the eye is at once caught 

 by the stout parapodia (Plate LX. 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, there- 

 fore, 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 LX. 

 fig. 2, neph.) These become less marked towards the anterior end, 

 and are absent from the first four or five pairs of parapodia l 

 (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. Eay 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 Arthropods 2 . 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. 



Eeturniug to the dorsal surface (Plate LX. 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 papillas are 

 stated to be absent from the first 8 segments, as is also the 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 Amphinomida;, 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. 



