THE HABITS AND STRUCTURE OF AREN1C0LA MARINA. 93 



The 5 per cent, formalin solution of the epidermal pigment is fluores- 

 cent, but does not yield any absorption bands, merely cutting off the 

 rays at the blue end of the spectrum. In successively thicker layers 

 of this solution, first the violet, then the blue, and lastly the green 

 portions of the spectrum were cut off. 



MacMunn (1889), however, has shown that the alcoholic extracts of 

 the integumental pigment shows a band in the blue and green (\ 

 503 —468) ; that the residue of this solution if dissolved in ether or 

 chloroform yields two bands \ 503 — 474, and X 465 — 446 ; and that 

 the residue of this solution again being dissolved in nitric acid gives 

 two bands, \ 500—468, and A 472 — 443, so that a chlorophan-like 

 lipochrome is present. It is probable that the pigment (melanin) of 

 the skin is derived from the .lipochrome of the yellow (i glandular" 

 tissue of the stomach, since the alcoholic extract of the latter yields a 

 similar absorption spectrum. 



Further investigation will be required to show in what way the 

 transference of the pigment from the yellow peritoneal cells to the 

 epidermis is brought about, and whether the dark coloured, hairy- 

 looking investment of the ventral vessel and its branches (PI. VII. , Fig. 

 5) contributes to the melanin of the skin. In this connection the inter- 

 muscular extension of the ccelom, bringing it almost into contact with 

 the epidermis at certain points, must be borne in mind (see p. 29). 



Selce. — The notopodial setae are long capillary structures averaging 

 6 mm. in length, and bearing several rows of minute free and pointed 

 hair-like processes (PI. VIII., Fig. 10). The neuropodia in the anterior 

 somites, which at first contain few setae, gradually extend by addition 

 of new ones at their ventral edge, so as to almost reach the mid-ventral 

 line (PI. 1, Fig. 1). By isolating the entire band of the setae the 

 different stages in their development may be seen. The youngest setae 

 are always at the lower end of the series ; the point of each seta is 

 formed first, then the toothed ridge, and lastly the shaft. The fully- 

 developed ventral seta is frequently almost smooth, owing to the 

 wearing down of the teeth behind the apex. The middle of the shaft is 

 straight, the inner end bent ventrally, and the outer end bent slightly 

 dorsally, ending with a finger-shaped process bordered on the convex side 

 by a toothed ridge, while on the concave side it is slightly produced at one 

 point into a minute process (PI. VIIL, Fig. 12, proc). This process is 

 more constant in the Laminarian than in the littoral variety. It 



