Page:Popular Science Monthly Volume 85.djvu/233

Rh with great rapidity when disturbed. They are often called "brittle stars," for if one seizes an arm it is promptly cast off, permitting the major portion of the animal to escape. Their beautiful sculpturing, rich colors, and the ornate patterns of their disks were admirably figured in color by Mr. E. M. Grosse, who executed more than 100 beautiful drawings which will serve to illustrate Dr. Clark's purposed paper upon the Echinoderms of Torres Straits. Indeed, Dr. Clark aptly called the region "a paradise for echinoderms," and it appears to be the richest known locality in the world for shallow-water forms of these animals, for Dr. Clark found 51 species at Maër Island alone, and in addition, he collected 26 others at Badu, Darnley and Thursday Islands; making 177 from Torres Straits. Thus his collection is a notable addition to that of the Museum of Comparative Zoology at Harvard, which was probably already the greatest gathering of specimens of echinoderms in the world. In almost every instance Mr. Grosse's figure is the only colored drawing of these Torres Straits species, and thus Dr. Clark's paper will be a classic upon the subject of tropical Pacific echinoderms.

117 species had been previously recorded from Torres Straits, and of these, Dr. Clark found only 42, but in addition he found at least 45 not previously known to science, so that at present fully 250 echinoderms are known from this extraordinary region.

As is well known to physiologists, the important subject of the penetration of living cells by alkalies has for several years engaged the attention of Dr. E. Newton Harvey, of Princeton, and his results essentially support Overton's lipoid theory, namely, that those substances which are most readily dissolved in fat-solvents enter living cells most readily; and this leads one to suspect that the cell surface may be lipoid, or fat-like in nature.

No one had been able to test this hypothesis for acids, until Dr. Harvey discovered a holothurian at the Murray Islands, Stycopus ananas, the intestines of which are purplish-red. If placed in acid, however, they turn bright red, and in alkalies dark purple; and these changes are reversible and may take place in weak acids or alkalies without killing the cells. Dr. Harvey used 24 different kinds of acids in dilute solutions upon this animal and found that those which are most poisonous penetrate most rapidly, and all the acids penetrate about in the ratio of their degree of toxicity. There is, on the other hand, no relation between the degree of dissociation of an acid and its rate of penetration of the living cells; and there is only a fair but by no means perfect agreement between the rate of penetration and the solubility of an acid in xylol.

Overton's theory applies, however, with the majority of acids, but the agreement is not perfect, and hence Harvey concludes that the power of penetration of an acid depends not only on its lipoid solubility but