464 GENERAL ZOOLOGY 



Articulate. To join; to unite by means of a joint. 



Artificial parthenogenesis. The development of an egg following artifi- 

 cial stimulation without the intervention of a sperm. 

 Assimilation. The transformation of digested and other absorbed food 



products into living substance, or into material that can be utilized by 



living substance. 

 Asymmetry. An arrangement of parts incapable of being divided by a 



plane into halves which are mirrored images of each other. 

 Atom. The smallest particle of a chemical element which can exist either 



alone or in combination with other similar atoms or with atoms of 



another element; the smallest particle of a chemical element which 



enters into the composition of a molecule. 

 Autonomic, autonomous. Self-governing; said of the sympathetic and 



parasympathetic nervous systems. 

 Axial. Pertaining to an axis. The backbone is the axial skeleton of 



vertebrates. 

 Axon. Process of a nerve cell conducting impulses away from the cell body. 

 Bacteria. A group of microscopic plants, some of which are the causative 



agents in the production of certain diseases. They exist in three general 



forms as follows: cocci, which are spherical; bacilli, rod-shaped; and 



spirilla, spiral filaments. 

 Barbel. A slender tactile process on the lips of certain fishes. 

 Biconcave. Hollow on each side or end. 

 Bilateral symmetry. An arrangement of parts capable of being divided 



by a plane into right and left halves. 

 Binomial nomenclature. The method of designating organisms by two 



names, one for the Genus and the other for the Species. Example: 



Rana pipiens, the leopard frog. 

 Biogenesis. The generally accepted principle that all living things are 



derived from living things; that only life reproduces life (see Abiogenesis). 

 Biogenetic law. In its modern form, the doctrine that an animal in its 



development repeats to a certain extent the history of its race. Also 



known as the law of recapitulation. 

 Biparental. Derived from two parents, male and female. 

 Biped. An animal which walks on two feet. 

 Blastocoel. The segmentation cavity within the blastula. 

 Blastomere. One of the cells formed in cleavage of the egg, fertilized or 



parthenogenetic. 

 Blastopore. The opening of the archenteron or gastrocoel. 

 Blastula. The stage during cleavage, when the cells are arranged in the 



form of a hollow sphere. 

 Buccal cavity. Mouth cavity. 



Carbohydrate. Sugars, starches, and cellulose. Organic compounds con- 

 sisting of carbon, hydrogen, and oxygen, the hydrogen and oxygen being 



in the same proportion as in a molecule of water (H 2 0). 

 Carnivore. A mammal belonging to the order Carninora. 

 Carnivorous. Flesh-eating. 

 Catabolism. The disintegrative phase of metabolism. 



