4S4 THE ORIGIN OF SPECIES 



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. — 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. 



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 earth-worms and the leeches. 



Antennae. — ^Jointed organs appended to the head in Insects. Crustacea 

 and Centipedes, 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 Centipedes). 



Asymmetrical. — Having the two sides unlike. 



Atrophied. — Arrested in development at a very early stage. 



Balanus. — ^The genus including the common Acom-shells which live in 

 abundance on the rocks of the seacoast. 



Batrachians. — A class of animals allied to the Reptiles, but undergoing 

 a peculiar metamorphosis, in which the young animal is generally 

 aquatic and breathes by gills. (Examples, Frogs, Toads, and 

 Newts.) 



Bowlders. — ^Large transported blocks of stone generally embedded in 

 clays or gravels. 



Brachiopoda. — A class of marine MoUusca, or soft-bodied animals, 

 furnished with a bivalve shell, attached to submarine objects by a 

 stalk which passes through an aperture in one of the valves, and 

 furnished with fringed arms, by the action of which food is carried 

 to the mouth. 



Branchle. — Gills or organs for respiration in water. 



Branchial. — Pertaining to gills or branchiae. 



