350 ME, A. G. BOURNE ON CEETAIN POINTS 



The margin is entire, and not fringed. 



In P. squamata (fig. 10) the surface in all the elytra is very rough, presenting large 

 granular conical lumps, especially developed in the outer and posterior regions of the 

 scale. Some of these granulations are red in colour, giving the rich grey colour which 

 the elytra possess in this species. The outer and posterior margins, and in the anterior 

 pairs the anterior margin also, are richly fringed with long processes, in addition to the 

 tactile papilke which are scattered over the surface. 



Prostomium. — The prostomium differs in shape in the two species (PL XXXVI. figs. 15 

 & 1G). In P. clava it is much more truncated anteriorly than in P. squamata. In the 

 latter species the prostomial tentacles are obviously mere prolongations from its anterior 

 edge. In P. clava the anterior portion is much smaller, and there is a tendency to form 

 a transverse ridge, giving the impression, from a dorsal view, that the lateral tentacles 

 spring from underneath the anterior edge of the prostomium. This they undoubtedly do 

 in many species of Polynoina ; but, from observations which I have made upon unde- 

 termined species collected at Naples and from the Norwegian Fjords, I have come to the 

 conclusion that there may be every transitional condition between these two extremes. 



Series of transverse sections have shown that these three tentacles are supplied with 

 nerves directly from the supraoesophageal ganglions, i. e. no doubt have an archi- 

 cerebral nerve-supply, and so are not of the nature of appendages, although they simulate 

 them in structure, but are mere prolongations of the prostomium ; they thus have funda- 

 mentally the same origin in the whole group. The anterior edge of the prostomium may 

 thin out into the bases of the tentacles ; it may be thicker, and tend to form a transverse 

 ridge, which may be produced and overhang the bases of the tentacles ; small points may 

 be formed here ; and, lastly, these may be carried far forward, and so completely hide the 

 origin of the lateral tentacles. If every intermediate condition between the two ex- 

 tremes can be found, these can hardly be used in generic distinctions. 



In P. squamata the anterior pair of eyes is much larger than the posterior pair, and lie, 

 as shown in PL XXXVI. fig. 15, very near them ; but in P. clava, while the posterior 

 pair have the same position, the anterior pair, which are of the same size, lie further 

 forward. 



First Body-Somite, Peristomial Somite (Huxley). — The most anterior somite of the body 

 possesses much-modified parapodia. A notopodial and a neuropodial lobe may, however, 

 be distinguished ; and each bears four setae. Huxley has described the existence of 

 similar structures in P. squamata (an acicula and two minute setae), and points out that 

 this fact, which Max Miiller * described in his account of the development of Polynoel 

 proves the peristomial cirri to belong to a modified somite. 



Second Body-Somite, or Buccal Somite.- — The second somite is also modified. The noto- 

 podial and neuropodial lobes are obscurely divided ; both aciculae are present ; the noto- 

 podial setae have the same general structure as in other somites, but the neuropodial setae 

 resemble the notopodial in structure rather than the neuropodial of other somites. 

 This fact, which appears to have been overlooked, is interesting as connecting the normal 

 parapodium with that of the much modified most anterior body-somite. 



* JIiiller's Archiv, 1851. 



