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THE AMERICAN NATURALIST [Vol. LIT 



The green pigment is readily extracted with fresh water. It 

 is not chlorophyll. When an animal is allowed to die in fresh 

 water, the integument and the ordinarily white internal parts 

 of the skeleton of a Mellita become bright green. Putrefactive 

 changes decolorize the green extract, and the color can not be 

 restored by alkali, or with HA- Green extracts are also de- 

 composed, irreversibly, by boiling. 



The green color is not seen in faintly acid fresh-water extracts 

 and the Mellita remains brown. If such an extract is made 

 alkaline, the green color promptly appears in the extract. The 

 substance responsible for the green hue in dead or injured parts 

 of Mellita is in fact a very good indicator. It is colorless in 

 aeid. vivid green in alkaline solutions; this color change may be 

 reversed many times. The "turning-point" of the indicator 

 is at an acidity of p H = 7.6-7.8— in a solution more alkaline 

 than neutrality, but well on the acid side of the reaction of sea 

 water (p /7 = 8.1 ±). This greening material seems to be pres- 

 ent throughout the body of Mellita, as freshly secured bits of the 

 (white) internal skeleton turn bright green in alkali. The few 

 available references to the coloration of clypeastroids indicate 

 that the alkali-greening substance regularly occurs in Clypeaster 

 and in other genera of this group. 



The ovaries of M. sesquiperforatus are heavily pigmented by 

 a substance of the " antedonin ' echinochrome " group. The 

 mature egg itself is linht brownish yellow, heavily yolked, and 

 apparently larger than any eehinoid egg that has been described. 

 It measures about 0.26 mm. in diameter, and is thus about twice 

 the size of the egg of M. testudinata (= pentapora) , which 

 measures 0.11 mm., though not so large as that of the brittle- 

 star Ophiodcrma, 0.30 mm. in diameter (Grave, 1916, p. 439). 

 The ovarian egg of M. sesquiperforatus is surrounded by a 

 gelatinous envelope, the whole being 0.35 ± mm. in diameter. 

 This envelope bears numerous evenly scattered clumps of pre- 

 cipitated reddish-purple pigment, the ovarian stroma being 

 densely crowded with similar " chromatophores. " In Echi- 

 mmtchnius the "chromatophores" of the egg-envelope are red 

 rather than purple. The purple pigment of the Mellita ovaries 

 exhibits the acid-alkali color changes and the absorption spec- 

 trum of the "echinochrome" pigments found in sea-urchins, 

 holothurians, crinoids, and even in star-fishes; a dilute extract 

 of a female Mellita may therefore be prepared which changes 



