GLOSSARY 



abdomen. In vertebrates that part of the trunk below or 

 behind the thorax; in invertebrates the posterior region 

 of the body. 



aboral. Opposite the oral or mouth region. 



achromatin. The material in the nucleus not colored by 

 certain dyes. 



adaptation. The condition of a portion of the body such 

 that it is adjusted or fitted to its functions. 



adductor. A muscle which draws some part toward the 

 middle line of the body. 



alga. Simple plants, one or many celled; without definite 

 leaves, stem or roots. 



alternation of generations. The alternation of sexual and 

 asexual forms in the life history of a plant or animal. 



alveolar. Resembling little cells or sacs, a common appear- 

 ance of protoplasm. 



amitosis. Simple or direct division of the nucleus, a mere 

 pinching into two parts. Opposed to mitosis or indirect 

 division. 



analogous. Similarity of function. 



anaphase. A stage in indirect division in which the chromo- 

 somes are pulled apart into two groups. 



anastomosis. The interjoining or fusing of nerves or blood- 

 vessels. 



animalcule. A microscopic animal. 



