BY WILLIUI A. IIASWELL, M.A., B.8C. 253 



calls was first pointed out by Ehlers* in Polynoe pellunda. I 

 have found it in most species which I have examined, though in 

 some cases the outline of the constituent elements were very 

 difficult to trace. 



(3). In focussing deeper than the upper layer of cells Ehlers 

 states that he could distinguish a series of dots which he repre- 

 sents as arranged in radiating lines, and which he regards as 

 indicating the existence of some tissue between the two layers 

 of cells. It has been assumed, by Quatrefages, and others, that 

 the scale is simply a flattened sac, between the two walls of which 

 is a cavity communicating with the cavity of the body. The evidence 

 in favour of this supposition is afforded by the fact that in certain 

 species specimens have been observed with all the scales distended 

 and globular, as if blown up by the pressure of fluid from within. 

 I have never seen this phenomenon, which would appear to be 

 of rare occurrence, but it is probably due to a forcible rupture 

 tearing the two layers of the scale apart and producing a 

 permanent malformation. Thus in Aphrodita the two membranes 

 of which the scale is composed are firmly united together by 

 fibrous tissue, and require some little force to effect their 

 separation. This fibrous layer is visible in the undissected scale, 

 and is seen still more distinctly when the layers are torn asunder, 

 when the bundles of fibres will be seen curled up on the inner 

 surface. The arrangement of the fibres, which are exceedingly 

 fine, varies in different species ; sometimes they are arranged in 

 definite wavy bundles ; sometimes the arrangement is quite 

 irregular, the fibres crossing one another in all directions. 

 Morphologically these fibres seem to represent the muscular 

 layer of the integument. 



In his account of the structure of the nervous system in 

 Aphrodita aeuleata] Quatrefages makes no mention of the 



* " Die Borstenwiirmer, p. 109, (1854)." 

 t xVuu. des Sciences Nat. (3me serie) t. xiv., p. 362, (1850.) 



