APHRODITA ACULEATA. 258 



due not to any change in outline, but to the play of light on the organs. The rainbow 

 lustre is lost on drying these hairs in a spirit-preparation, but is again restored on 

 immersion in water. De Saint-Joseph (1888) thinks Kriikenberg : was wrong in con- 

 sidering the felt was like chitin ; it is more like keratin. 



The lustrous brown spines spring in a fan-shaped series from the middle of the 

 foot, and form slightly curved sharp weapons of defence. They end in an acute two- 

 edged tip, and readily pierce the skin. They have the same brittle chitinous structure 

 as t^he other spines in this species. 



In young specimens the dorsal spines are longer, more tapered and curved, and 

 meet in the middle of the dorsum so as to guard the back, as in other Aphroditidae. 

 These and the rest of the spines are also often of a lighter golden hue. The thin and 

 comparatively even Coating of felt which covers the dorsum of some young specimens 

 gives a character to such examples on clean ground, as off the west sands at St. 

 Andrews. A great change ensues in these bristles during growth. Small specimens 

 from a quarter of an inch upward to an inch appear to be common on muddy ground, 

 and are densely coated with it, — as, for instance, in St. Magnus Bay, between the 

 Skerries and Fetlar, and the Fjords of Norway (Canon Norman). On sandy ground, on 

 the other band, they are beautifully clean, and the long golden spines curve as guards 

 over the dorsum. 



The first foot bears a dense tuft of simple, slightly iridescent, slender, hair-like 

 bristles, chiefly directed upwards and forwards. In the middle is another fan-shaped 

 series directed forward and slightly curved (convexity outward). Below is a third 

 group of similar structure, probably representing the ventral series, directed downwards 

 and forwards, and with their convexity (for they are stiffish) downwards. On the outer 

 side of the bases of the first two series are the tentacular cirri. This foot shows no 

 marked division into dorsal and ventral parts, but has a somewhat clavate outline. 



The second foot has the ventral division separated. Dorsally the rounded boss has 

 externally a dense series of stiff hairs, which stand out in a fan-shaped manner, while 

 towards the dorsal median line (Plate XXXV, fig. 25) the second or adjoining series are 

 modified to form the very slender hairs of which the felt is composed. The ventral 

 division bears smooth spines (Plate XXXVI, fig. 18), and inferiorly the tuft of some- 

 what stiff, pinnate bristles (Plate XXVI, fig. 17). 



The ventral division of each typical foot, as noticed by Baster and Swammerdam, 

 bears three series of bristles arranged in transverse rows (Plate XXXVI, figs. 10 and 22). 

 The strongest occur dorsally, and consist of about three powerful dark brown bristles 

 (Plate XXXVI, fig. 2 c), flattened at the tip, which varies in condition, though funda- 

 mentally the type is somewhat hastate, as observed in the posterior region of the body 

 (Plate XXXVI, fig. 20). In front view (a) the tip resembles a broad spear, sometimes 

 asymmetrical ; in lateral view, again, the tip (b) is more or less tapered, and posteriorly 

 has a slight dilatation at the commencement of the shaft. 



The middle series (Plate XXXV, fig. 25 b) has the same type, but the bristles are 

 paler and more numerous, about eight occurring in the row. The curvature at the tip is 

 more distinct. Posteriorly the hastate condition^ evident (Plate XXXVI, fig. 19). 



1 ' Vergleichende physiol. Stud./ 2e ser., part 1, p. 54, Heidelberg, 1882, 8vo. 



