492 



SCIENCE 



[N. S. Vol. XXVII. No. 691 



uneven than in the ordinary form, for it 

 is more strongly areolated and the 

 branchial areas are more swollen, so that 

 the vertical thickness is greater and the 

 reticulated areas of the sides are broader, 

 giving a larger surface for aeration of the 

 water, and indicating larger gill-cavities 

 and gills. The dorsal surface of the cara- 

 pace is covered with more numerous and 

 larger granules, bearing numerous short 

 dark hairs, very evident under a lens of 

 low power, and capable of holding ad- 

 herent dirt. 



The ambulatory legs are distinctly larger 

 and longer than in the common form. The 

 proportion of the merus joints of these legs 

 to the breadth of the carapace is 1 :1.36. 

 In Ricordi, 1 :1.5. 



The colors, when living, appear dull or 

 sordid yellowish brown, or mud-color, due 

 partly to adherent dirt, but often specked 

 or mottled with red or reddish brown. 



It is not improbable that it has the habit 

 of eating diiferent food from its parent 

 species, and also a somewhat different 

 breeding season, so that the two forms may 

 no longer interbreed. This could not be 

 determined at the season of the year when 

 we were in Bermuda. 



The young crabs, moulting from the 

 megalops at the shore, have evidently in- 

 herited the instinct to seek the higher and 

 drier localities, where they probably have 

 fewer enemies. The modifications that 

 have taken place are in accordance with 

 the change in habitat. The increased 

 hairiness of the carapace and legs serves to 

 retain the dirt that aids materially in their 

 concealment when exposed. Probably they 

 feed mostly at night. The larger gill 

 capacity and longer legs have evident ad- 

 vantages. 



That it is not a casual or transitory vari- 

 ation is evident from the fact that there 

 are, in the museum of Yale University, 



several good, characteristic, adiilt specimens 

 sent to us before 1866 (perhaps collected 

 as early as 1855), by J. Matthew Jones, 

 Esq., who resided in Bermuda for many 

 years, during the colder seasons, and whose 

 first book on Bermuda was published in 

 1859. 



The evolution and habits of this race of 

 crabs would furnish a good subject for in- 

 vestigation by some one connected with the 

 Bermuda Biological Station. The varietal 

 or subspecific name, terrestris, indicating 

 its marked terrestrial habits, is given to it 

 by the author. 



The Meawing of the Color Variations of 

 Litorina palliata: F. B. Sumner and 

 Jas. W. Undeewood. 

 This moUusk offers a striking example of 

 apparent protective coloration, nearly all 

 of its varieties harmonizing beautifully 

 with one or another part of the rock weed 

 on which it dwells. This resemblance re- 

 lates not only to the general color, but to 

 the shape of the shells, which, on their 

 natural background, strongly suggest the 

 floats of the weed. On analysis, however, 

 the popular explanation of the phenomenon 

 as due to the natural selection of the more 

 favorably colored individuals, seems far 

 from certain. (1) There is no tendency 

 whatever for the mollusk to choose a back- 

 ground resembling its own particular color 

 rather than one conspicuously unlike it. 



(2) In nature, the red and brown shells are 

 found statistically to be present in about 

 the same proportions on the Ascophylliim 

 as on the Fucus, although the latter alone 

 displays red or brown tints in its foliage. 



(3) The green element in the color of many 

 of the shells, which is an important factor 

 in bringing about the harmony with their 

 surroundings, is found to be due to certain 

 algffi inhabiting their siiperficial layers. It 

 is thus an entirely adventitious color, and 

 these same algae are found in abundance on 



