GLOSSARY 525 



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-phol'-o-gy. The science which deals with structure and 



form. 

 Mtts'-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'-rtjs. 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 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. 



