GLOSSARY 



OF THE 



PRINCIPAL SCIENTIFIC TERMS USED IN THE 

 PRESENT VOLUMES 



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 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 

 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 coloring matters 

 characteristic of the species have not been produced in the skin and 

 its appendages. Albinism is the state of being an Albino. 



Algjs. — 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 wbich 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. 



Ammonites. — A group of fossil, spiral, chambered shells, allied t 

 the existing pearly Nautilus, but having the partitions between the 

 chambers waved in complicated patterns at their junction with the 

 outer wall of the shell. 



Analogy. — The resemblance of structures which depends upon simi- 

 larity of function, as in the wings of insects and birds. Such struc- 

 tures are said to be analogous, and to be analogues of each other. 



Animalcule. — A minute animal : generally applied to those visible 

 only by the microscope. 



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

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

 terms 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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