358 Glossary 



into a spindle and chromosomes; the latter split and the halves move 



to the poles of the spindle where they form the daughter nuclei. 

 MODIFYING FACTORS. Factors whose principal influence is seen in modifying 



other factors or the characters to which they give rise. 

 MON-O-HY'-BRID. The offspring of parents differing in one character. 

 MON'-O-TREMES. The lowest group of mammals, including the duck-bill 



and the spiny anteater. 



MOR-PHOI/-O-GY. The science which deals with structure and form. 

 MUS'-CA. A genus of flies including the house-fly. 

 MU'-TANT. A sudden variation or sport which breeds true. 

 MU-TA'-TIONS. Inherited variations which are more or less striking; 



"sudden variations," "sports." 



NEC-TU'-RUS. A large salamander; the mud-puppy. 

 NEM'-A-TODE. A round-worm or thread-worm. 

 NE'-RE-IS. A marine annelid, or ringed worm. 

 NEURAL GROOVE. The groove on the dorsal surface of the embryo of a 



vertebrate which develops into the brain and spinal cord. 

 NEURAL TUBE. A tube formed from the neural groove and giving rise to 



brain and spinal cord. 



NO'-TO-CHORD. The cellular rod which forms the basis of the backbone. 

 NU'-CLE-US. The central organ of a cell, composed of chromatin and 



achromatin. 

 NULLIPLEX FACTORS or CHARACTER. A condition in which a character is 



absent because its determiner is found in neither parent. 

 ON-TOG'-E-NY. Development of an individual. 

 O'-O-CYTE. The ovarian egg before maturation (formation of polar 



bodies). 



O-O-GEN'-E-SIS. The development of an ovum from a primitive sex-cell. 

 O-O-GO'-NI-A. The earliest generations of cells which produce ova; pri- 

 mordial egg cells. 



O'-O-SPERM. The fertilized egg after union of egg and sperm. 

 ORDER. The chief sub-division of a class. 

 ORGANIZATION. Differentiation and integration, i.e., different parts united 



into one whole. 



OR-GAN-OG'-E-NY. The formation of various organs of the body. 

 OR-THO-GEN'-E-SIS. The doctrine that the course of evolution is definitely 



directed by intrinsic causes. 

 O-VI-PAR'-I-TY. Young brought forth as eggs, i.e., in an early stage of 



development. 

 O'-VULES. The female sex cells of flowering plants with the immediately 



surrounding parts. 



