GLOSSARY 509 



MOR-PHOL'-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. 



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

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

 NE'-HE-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 chro- 



matin 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; primordial 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-XY. 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. 



