818 GLOSSARY 



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. 



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. 



Analogy. — That resemblance of structures which depends 

 upon similarity of function, as in the wings of insects 

 and birds. Such structures 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. 



Annelids. — A class of worms in which the surface of the 

 body exhibits a more or less distinct division into rings 

 or segments, generally provided with appendages for 

 locomotion and with gills. It includes the ordinary 

 marine worms, the earthworms, and the leeches. 



Antenna. -Jointed organs appended to the head in In- 

 sects, Crustacea and Centipeds, and not belonging to 

 the mouth. 



Anthers. — The summits of the stamens of flowers, in which 

 the pollen or fertilizing dust is produced. 



Aplacentalia, Aplacentata, or Aplacental Mammals. 

 See Mammalia. 



Archetypal. ^ — Of or belonging to the Archetype, or ideal 

 primitive form upon which all the beings of a group 

 seem to be organized. 



Articulata. — A great division of the Animal Kingdom 

 characterized generally by having the surface of the 

 body divided into rings called segments, a greater or less 

 number of which are furnished with jointed legs (such as 

 Insects, Crustaceans and Centipeds). 



