EN" THE A>"ATO:MT OF THE POLENOENA.. 351 



This second body -somite appears to be the first elytron-bearing somite in all Polynoina. 



The nenropodial cirrus is much modified, resembling a notopodial cirrus in size 

 and shape, is bent inwards towards the mouth tag. 1, bue. cr.\ and is the buccal cirrus 

 XLaberg.). There can be no doubt that this buccal cirrus is a modified neuropodial 

 cirrus ; and the possibility of a neuropodial cirrus simulating a notopodial (we have seen 

 a similar ease in the prostomial tentacles simulating notopodial cirri ) is of irreat import- 

 ance to us in considering the homology of the pygvdial cirri. 



Palps. — The palps ditfer from all the other tentacular struct;. 3 being muscular 

 along their whole length. They are capable of great elongation and contraction. 



In P.sgvamata they are smooth: but in P. ; they have six longitudinal rows of 



tactile papilla?, each provided with its sensory hair. 



These palps present more difficulty than do any of the other tentacles or cirri. They 

 originate (sections of P. (Sarmothoe) areolata) just where the prostomium joins the 

 peristomial and buccal somites, although they appear to have more connexion with : 

 prostomium than with the other somites. Their nerve-supply appears to come from the 

 snpracesophageal iranslion. Their prostomial connexions are borne out when we com- 

 pare them with similar organs in such simple forms as the SyUidae, where they are 

 evidently prostomial, sprii - ° . . ie, loc. cit.) from its ventral surface. 



This view is completely borne out by Max Muller's * account of their development. 



Pygydial Somite. — The terminal somite is very much reduced, and appears merely - 

 support for the pygidial cirri. These resemble notopodial cirri in size and structure. 

 They are well developed in both species under consideration : but in nianv species of 

 Polynoina they are quite small. In such forms the anus is terminal ; but where they are 

 so strongly developed the anus is pushed forwards, and comes to lie on the dorsal 

 surface. 



I have found in two or three specimens of P. clava an acicula (fig. 6) running 

 dorsally, and perforating a well-marked papilla, as do the other acicula?. In other speci- 

 mens, of which I have examined a large number with this special point in view, there is 

 a trace of such a structure ; but in the majority all trace is gone; possibly the acicula 

 drops out while the animal is thus quite young. 



In other undetermined species of Polynoe which I have examined there is. as a rule, 

 a small acicula in some, a small acicula accompanied by rudimentary setae in others, 

 in the pygidial segment, most strongly marked where the segment is little modified. 

 The presence of these structures seems to me of great interest, as showing that the 

 pygidial cirri are the neuropodial (as they are ventrad of the acicula, whether that be 

 neuro- or notopodial) cirri of a much-modified somite, a pygidial somite. Further, just 

 as we found the second body-somite presented a connecting link between the first. 

 the peristomial segment, and the other somites, so in the penultimate somite we find 

 that the seta? are few in number, and not strongly marked in character, connecting the 

 pygidial somite with those in front of it. 



Nephridial Papilla and Nephridia. — Minute and detailed as many of the systematic 

 descriptions of various species of Polynoina are, it is not a little curious that the exist- 



5 Max Miiiler, Miillers Archi , 1S5] 



