IN THE ANATOMY OF THE POLTNOINA. 349 



Parapodia. — The parapodia in the central region are normal, but at either end of the 

 body they become modified. The normal parapodium consists of notopodiiun and neuro- 

 podium, the latter being about four times the size of the former, which, however, in 

 P. clava cannot be regarded as a mere tubercle projecting from the upper surface of the 

 neuropodium (Huxley, P. squamata), but more nearly retains its normal position as a 

 lobe of the parapodium corresponding to the neuropodial lobe. 



The notopodial acicula is well developed. The notopodial seta? are about twelve in 

 number ; but this number is by no means constant, as they are continually falling out and 

 being replaced by new ones ; consequently setae of various stages of growth may be 

 found in one parapodium ; there appear, moreover, to be permanent varieties in the 

 notopodial series. Figs. 12, 12 a, 12 b, & 12 c represent such varieties of the notopodial 

 seta? of P. squamata (only the extremities are drawn). Figs. 12 & 12 a come from 

 short seta3, figs. 12 b & 12 c from very long ones. In the short seta? there are about 

 25 pectinated frills, which encircle in the central region about two thirds of the cir- 

 cumference of the blade ; but the upper frills, which are more pectinated, encircle much 

 less, and the lower ones rather more ; there is only one longitudinal series of frills. 

 The long seta? present series of frills which are not so well developed. The notopodial 

 seta? of P. clava are all formed upon the type shown in fig. 11, corresponding to the 

 long seta? of P. squamata. 



The neuropodial setae are very similar in two species (PI. XXXV. figs. 13 & 14). There 

 are two longitudinal rows of 7 or 8 pectinated frills placed opposite to one another^ 

 although the fact that the ends of the frills running slightly downwards may give in some 

 series the appearance of the frills alternating on the two sides. The distal rows of frills 

 are more strongly developed than the rest, and present five large teeth upon their free 

 edge. In P. squamata the central tooth is relatively much larger than in P. clava. The 

 proximal frills are always feebly developed. 



The neuropodial acicula pierces a small papilla; dorsad of this papilla there are 

 about six neuropodial seta?, and ventrad about twice that number. This, as Grube 

 points out, is the usual arrangement — twice as many seta? ventrad as dorsad of this 

 papilla. 



The notopodial cirrus is more bulbous below the point in P. clava than in P. squamata. 



The neuropodial cirrus of P. clava differs from that of P. squamata in the same way 

 that the notopodial cirrus does, and is besides shorter and rather stouter. 



The papilla (pyriform tubercle of Huxley, ventral papilla of Grube and Ehlers, figured 

 occasionally without description by Claparede and Malmgren) which I propose to 

 call the uephridial papilla, springs, as Huxley pointed out, not from the parapodium, but 

 from the neural surface of the somite itself. 



Elytra.— -The elytra present various shapes, according to their position, in both species. 

 The shape also varies in individuals, as will be seen by comparing figs. 3 & 4, PI. XXXIV. 



The anterior pair vary in shape between an oblong with rounded corners (fig. 7) and a 

 broad ovate (fig. 4). 



The three anterior pairs present a slight roughness on the surface ; but the posterior 

 pairs are almost smooth. 



49* 



