440 ELEMENTS OF BIOLOGY 



Ampulla. The bulbs at the extremities of the semicircular canals in 

 vertebrates, in which are located the otoliths and the nerve endings 

 that when stimulated record the sense of balance. 



Amylase. A sugar-digesting enzyme in the vertebrate small intestine. 



Anabolism. Metabolic processes that are constructive in nature. 



Anaerobe. An organism that lives in the absence of atmospheric oxygen. 



Anesthesia. A reversible decrease in irritability. 



Anaphase. An arbitrary stage in the process of mitotic cell division 

 characterized by the migration of the chromosomes toward opposite 

 centrosomes. 



Anatomy. The science of structure. 



Animal Biology. The principles of Biology as shown in the lives of 

 animals. 



Animal pole. If one considers the egg as a sphere the term animal pole 

 refers to that pole of an egg most active in starting development; 

 cleavage planes start at the animal pole. The animal hemisphere 

 usually contains less yolk than does the more sluggish vegetal hem- 

 isphere. 



Animal sociology. The relations of animal life within a geographical 

 area. 



Anther. The structure on the end of the stamen of the flower in which 

 the microspores are produced. 



Antheridium. That structure in the plant body which produces the 

 sperms. 



Antibody. Any substance produced by the host to neutralize {X)isons 

 or to destroy invading bacteria. 



Antitoxin. A substance produced by the host which neutralizes the 

 poisons of invading pathogenic bacteria. 



Archenteron. The primitive gut, formed in development when gastru- 

 lation takes place. 



Archegonium. That structure in the plant body which contains the egg. 



Artificial immunity. The immunity resulting when the body has been 

 treated with vaccines or serums. 



Aster. The form assumed by the centrosome and the rays appearing 

 about it during mitotic division. 



Astigmatism. A disorder of the eye involving defects in the symmetry 

 of the lens. 



Atom. The ultimate minute particle of a substance that cannot be fur- 

 ther divided without changing the character of the material; for 



