GLOSSARY 



OF THE 



PEINCIPAL SCIENTIFIC TEEMS USED IN THE 

 PEESENT VOLUME.* 



Abbrhant. — Forms or groups of animals or plants wHct 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. 



Abehration (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 colored rays are separated by 

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

 at different distances — this is cJiromatic 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 tennis 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. 



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

 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. 



*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 

 Bome 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. 



