348 ME. A. G. BOUENE ON CEETAIN POINTS 



clavus, " since lie does not distinguish it from the latter while contrasting it with 

 L. squamatus." P. squamata, as Malmgren has pointed out, is not found in the Mediter- 

 ranean ; while, at any rate at Naples, P. grubiana is the commonest of the Polynoina. 

 I have collected there about a hundred specimens ; and thus, while I am convinced that 

 it is the same species as our P. clava, I have been startled to observe the great individual 

 variation which may occur in a single species. 



The Mediterranean forms possess rather darker scales, but possess in other places less 

 pigment than do the specimens we had obtained from Devonshire ; they are moreover 

 considerably smaller. 



My observations upon the series of P. clava have led me to classify their characters 

 thus : — 



Variable. 



Size and shape of the body. 



Elytra, in respect of their size, shape, and tint. 



Amount of medio-dorsal region of back covered 

 by them ; extent to which each overlaps the 

 following elytron ; firmness of their attach- 

 ment to the body. 



Thickness of the anterior margin of the pro- 

 stomium, influencing the apparent place of 

 origin of the lateral tentacles. 



Amount of pigment on the body-surface. 



Presence of acicula in the pygidial segment. 



Constant. 



Number of segments in the body. 



Number of elytron-bearing segments. 



Structure of median tentacle. 



Structure of lateral tentacles. 



Structure of palps. 



Shape of equivalent parapodia. 



Structure of the notopodial and neuropodial cirri. 



Structure of the ventral tubercles (nephridial 

 papillae) . 



Character of equivalent setse. 



Fringing of the margin of the elytron (not in- 

 cluding the tactile papilla?) . 



Position and size of the eyes. 



Mode of origin of the median prostomial tentacle. 



Position of the anus. 



Structure of pygidial cirri. 



The following variations are also to be found in one and the same individual : — 



Structure of the notopodial and neuropodial setse ; their length and number. 

 The elytra in respect of size, shape, and amount of granulation on their surface. 

 The shape of the parapodia. 

 This individual variation necessitates great care, in making comparisons between these 

 forms, that exactly ecurivalent structures be compared. 



Polynoe clava, Montagu. 



Shape of the Body. — As I have pointed out, we can attach very little importance to such 

 difference in the shape of the body as Johnston has described as existing between P. squa- 

 mata and P. clava ; my specimens of P. clava show much more variation among themselves 

 (compare figs. 3 & 4, PI. XXXIV.). Still less can any importance be attached to the 

 position of the elytra with regard to the medio-dorsal region ; whether these latter do 

 not meet, simply meet, or overlap, depends entirely upon the amount of food in the 

 alimentary canal and the number of ova contained in the body-cavity. Figs. 3 & 4 show 

 two extremes in this respect. 



The body consists of a prostomial lobe with its tentacles and 27 somites ; the 1st of these 

 is the peristomial somite (Huxley), the 2nd the first elytron-bearing somite, and the 

 27th the pygidial somite. All these segments bear more or less modified parapodia. 



