GLOSSARY 



OF THE 



PRINCIPAL SCIENTIFIC TERMS USED IN THE 

 PRESENT VOLUME.* 



Aberrant. — Forms or groups of animals or plants which deviate 

 in important characters from their nearest allies, so as not to be 

 easily included in the same group with them, are said to be 

 aberrant. 



Aberration (in Optics). — In the refraction of light by a convex lens 

 the rays passing through different parts of the lens are brought 

 to a focus at slightly different distances, — this is called spherical 

 aberration ; at the same time the coloured rays are separated by 

 the prismatic action of the lens and likewise brought to a focus 

 at different distances, — this is chromatic aberration. 



Abnormal. — Contrary to the general rule. 



Aborted. — An organ is said to be aborted, when its development 

 has been arrested at a very early stage. 



Albinism. — Albinos are animals in which the usual colouring 

 matters characteristic of the species have not been produced in 

 the skin and its appendages. Albinism is the state of being an 

 albino. 



Algm. — A class of plants including the ordinary sea-weeds and the 

 filamentous fresh-water weeds. 



* I am indebted to the kindness of Mr. W. S. Dallas for this 

 Glossary, which has been given because several readers have com- 

 plained to me that some of the terms used were unintelligible to them. 

 Mr. Dallas has endeavoured to give the explanations of the terms in 

 as popular a form as possible, 



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