252 APHRODITA ACULEATA. 



aspect (Fig. 17), the caeca forming voluminous organs in the body of the Annelid. 

 Pallas found nothing in the proboscis (his ventriculus), whereas in the gut he met with 

 particles of fuci. In many at St. Andrews and elsewhere mud of various degrees of 

 darkness occurs in the canal and its branches. Swammerdam thought the ramifica- 

 tions of the intestine anastomosed with each other. 



Scales. — The overlapping, irregularly rounded scales x number fifteen pairs, and are of 

 considerable size. The first two show a narrow external margin beyond the pedicle, but 

 in the rest the latter occurs at the external border, and it is proportionally large 

 throughout, the scale being thus firmly adherent over an extensive surface while readily 

 moved by the muscles of the parts. The surface of the cuticle on the dorsum and the 

 scale-pedicle is minutely papillose, but the scale proper is smooth, only a few minute 

 papillae occurring along the edge. They are often coated with patches of a blackish- 

 brown granular deposit. The size of the scales does not always seem to correspond pro- 

 portionally with that of the specimen. Many of the older authors, like Swammerdam, 

 considered these organs the gills. 



Dorsal Fimbriated Papillse. — On the dorsum of the sixth foot an elevated ridge at the 

 posterior border, rather beyond the line of the scale-pedicles, gives origin to a short 

 process with a thin, flat, fimbriated extremity, generally of three divisions. The terminal 

 fimbriae of the papillae become more complex and the process longer as we proceed 

 backwards, the organs appearing, after the sixth, on the eighth, tenth, and every 

 alternate foot (devoid of scales) to the twenty-sixth, when they occur on the twenty- 

 seventh and the last, a small one on the twenty-ninth, that is on the foot behind the last 

 scale. These organs have been interpreted as branchiae by Pallas, Savigny, Kinberg, 

 and others; while many, such as Cuvier, Carus, Duvernoy, and Oersted, held that the 

 scales were respiratory organs. The great thickness of the cuticle of these processes, and 

 the absence of large blood-vessels, as De Quatrefages showed, do not favour the view that 

 they are special branchial structures, though the lobes of the alimentary caeca come close 

 to them. The cuticle occasionally may be comparatively thick on the surface of 

 branchiae, as in certain Buphrosynidae, but it does not attain the great density seen in 

 these processes of the sea-mouse. 



Feet.— The structure of the foot is shown in Plate XXXVI, fig. 10 (representing the 

 tenth foot), and the organ in the various regions of the body conforms to the same pattern. 

 The dorsal division bears the beautiful iridescent hairs, which gleam with all the beauty 

 of a permanent rainbow. A dense and most gorgeous tuft of these, thicker than the 

 dorsal series, occurs just above the ventral division of the foot, and extends more or less 

 to the dorsal edge of the spines, where another dense tuft of hairs, less brilliant than the 

 first series and much finer, occurs, and which form the felt on the dorsum.. This property 

 of felting does not appear to be due to any roughness of the exterior of these fine hairs, 

 though fracture may render such rough, but to their flexible and attenuated condition. 

 The tips of the hairs are often curved (see Plate XXXY, fig. 27). The first-mentioned 

 series are brittle and gorgeously iridescent, the tips under a lens being wavy, a feature 



1 Darwin was of opinion that these were homologous with the wings and elytra; of insects, ff and 

 it is not improbable that with our existing insects, organs which at an ancient period served for 

 respiration have actually been converted into organs of flight." Unfortunately, proof is deficient. 



