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 slightl}^ different dis- 

 tances — this is called spherical aberration; at the same 

 time the colored rays are separated by the prismatic 

 action of the lens and likewise brought to a focus at dif- 

 ferent distances — this is chromatic aberration. 



Abnormal. — Contrary to the general rule. 



Aborted. — An organ is said to be aborted when its devel- 

 opment has been arrested at a very early stage. 



Albinism. — Albinos are animals in which the usual color- 

 ing matters characteristic of the species have not been 

 produced in the skin and its appendages. Albinism is 

 the state of being an albino. 



Alg^. — 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, wliich 

 has been given because several readers have complained to me that some of the 

 terras used were unintelligible to them. Mr. Dallas has endeavored to give 

 the explanations of the terms in as popular a form as possible. 



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