THE U^^IYERSE A SERIES OF CHAN-GES. 237 



containing in most races of men more or less pigmentary 

 matter, which gives the skin its various shades from black 

 to white. It is penetrated b)^ the ducts of the skin's sweat- 

 glands and oil-glands ; becomes hard in palms of hands; 

 otherwise is soft. The hair and nails are modifications of it. 

 On leaves it is penetrated by the stomata, transmitting 

 exhalations and absorbing carbonic acid, the most important 

 part of plant food. /^^-^^ 



Epithe'lium. (Soft, delicate, tender.) The layer of cells lin- 

 ing serous (closed) and mucous (open) cavities, the mucous 

 epithelium being continuous with the epidermis. (Mucous 

 is formed by the bursting of epithelial cells.) Illd. 



Esoph'agus. The gullet. Extends from pharynx to stomach. 

 Ethmoid. Sieve-like. The ethmoid lone is one of the eight 

 bones which compose the cranium, so called because its up- 

 per plate is pierced by numerous holes. It is situate at the 

 anterior, inferior, and middle part of the cranium. 

 Evolu'tion. According to the hypothesis of evolution, in its 

 simplest form, the universe as it now exists is the result 5f 

 "an immense series of changes," related to and dependent 

 upon each other, as successive steps, or rather growths, con- 

 stituting a progress'; analogous to the unfolding or evolving 

 of the parts of a living organism. Evolution is defined by 

 Herbert Spencer as consisting in a progress from the homo- 

 geneous to the heterogeneous, from general to special, from 

 the simple to the complex ; and this process is considered to 

 be traceable in the formation of the worlds in space, in the 

 multiplication of the types and species of plants and animals 

 on the globe, in the origination and diversity of languages, 

 literature, arts, and sciences, and in all the changes of human 

 institutions and society. Henry Hartshorne. 



The animal kincrdom displays a unity of plan or a correla- 

 tion of parts by which common principles are traced through 

 the most disguising diversities of form, so that in aspect, struc- 

 ture, and functions the various tribes of animals pnss into 

 each other by sliirht and gradual transitions. The arm of a 

 man, the fore limb of a qnndrunod, the wing of a bird, and 

 the fin of a fish are homologous, thnt is, they contain the 

 same essential parts, modified in correspondence with the dif- 

 ferent circumstances of the animal ; and so with the other 



