GLOSSARY 



OF THE 



PRINCIPAL SCIENTIFIC TERMS USED IN THE 

 PRESENT VOLUME 1 



Aberrant. — Forms or groups of animals or plants which deviate in im- 

 portant characters from their nearest alUes, 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 aber- 

 ration; 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 development has 

 been arrested at a very early stage. 



Albinism. — Albinos are animals in which the usual coloring 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. 



Alternation of Generations. — ^This term is applied to a peculiar 

 mode of reproduction which prevails among many of the lower 

 animals, in which the egg produces a living form quite different 

 from its parent, but from which the parent-form is reproduced by 

 a process of budding, or by the division of the substance of the first 

 product of the egg. 



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

 which has been given because several readers have complained to me that 

 some of the terms used were unintelligible to them. Mr. Dallas has endeav- 

 ored to give the explanations of the terms in as popular a form as possible. 



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