444 APPENDIX 



MICROSPOROPHYLL. A modified leaf, of a heterosporous sporo- 

 phyte, which produces microspores. A stamen. 



MITOSIS. The typical process of cell division. 



MODIFICATIONS. In genetics : changes in the soma due to environ- 

 mental influences; so-called acquired characters are modifica- 

 tions. In evolution : signifies ' change ' ; no technical connotation. 



MONOHYBRID. The progeny of parents differing in regard to one 

 given character. 



MORPHOGENESIS. The origin of the form and structure of an organ- 

 ism during ontogeny. 



MORPHOLOGY. The science of the form of animals and plants. 



MOSAIC INHERITANCE. Inheritance of a character in part from each 

 parent but without blending. 



MUTATION. A heritable variation due to a fundamental change in 

 the constitution of the germ plasm, independent of the normal 

 processes of segregation and crossing-over. 



MYOTOMES. Muscle segments in body wall of lower Vertebrates 

 and embryos of higher forms. 



NATURAL SELECTION. The processes occurring in nature which 

 result in the "survival of the fittest" individuals and the elimi- 

 nation of those less adapted to the conditions imposed by their 

 environment and mode of life. 



NEPHRIDIUM. An excretory organ; e.g., in Earthworm. 



NEPHROSTOME.' Coelomic opening or funnel of a nephridium. 



NERVE. Essentially a group or cable of parallel nerve fibers bound 

 together. See Axon. 



NEURAL CANAL. The tube in which the brain and spinal cord lie. 

 Formed by the neural arches and centra of the vertebrae. 



NEURAL TUBE. A tube derived from the ectoderm and forming 

 the brain and spinal cord in Vertebrates. 



NEURON. A nerve cell, comprising cell body and cytoplasmic pro- 

 cesses. See Axon. 



NITRIFYING BACTERIA. Types of Bacteria which, in the process of 

 their nutrition, change ammonia (NH 3 ) into compounds with the 

 N0 2 radical (nitrites), and change nitrites into compounds with 

 the N0 3 radical (nitrates.) 



