390 BIOLOGY 



atrophy (Gr. a = without + trephein = to nourish). To decrease in size 

 as the result of disuse, or from other causes. 



auditory. Pertaining to hearing, 194. 



auricles (Lat. auris = ear). The chambers in the heart that receive 

 venous blood, 188. 



automatic activity. Actions started by the organisms and not brought 

 about by any external stimulus: spontaneity, 3. 



autophytes (Gr. autos = self + phyton = plant). Plants which subsist 

 upon minerals and gases, which they utilize through the agency of sun- 

 light, 226. 



available energy, 298. 



avidity for water, 127. 



axial. Pertaining to the axis. 



axial skeleton. The skull and spinal column, with the ribs and sternum, 

 177. 



axil. The angle above the attachment of a leaf. 



axis cylinder. See axon. 



axon. The process from a neuron extending outward and becoming the 

 axis cy Under of a nerve fiber, 170. 



bacillus. A motile, rod-shaped bacterium. 



bacteria. A group of extremely minute plants, the simplest and smallest 

 known organisms, 26, 80, 232, 235. 



ball-and-socket joints, 185. 



barriers. Factors that check the distribution of organisms, 380. 



basioccipital, 180. 



bast. The fibers of the phloem. 



bees, parthenogenesis in, 246. 



bell animalcule. Same as Vorticella. 



biennials (Lat. bi- = twice + annus = year). Plants that live two years, 

 growing the first year and fruiting the second. 



bilaterally symmetrical. Having the two sides strictly counterparts of 

 each other, 155. 



bile. The secretion of the liver; also called gall, 186. 



biogenetic law (Gr. bios = life + genesis = creation). The law that em- 

 bryology tends to repeat past history, 290. 



biological sciences, classification of, 18. 



bladder, 199. 



blade of leaf, 114. 



blastula. A hollow-sphere stage of the developing egg. 



blend. To mix, as when the offspring shows characters midway between 

 those of its parents, 362. 



blights, 232. 



