370 GLOSSARY 



Opposable: A term applied to the thumb or great toe when 

 they are capable of being placed with their tips opposite 

 to those of the other digits. 



Organelle: Literally, a "miniature organ," i.e., one of the 

 living components of a cell as distinguished from the meta- 

 plastic or non-living inclusions. 



Oxy chromatin: That portion of the nuclear network which 

 stains with acidic dyes, the finer nuclear reticulum in 

 which the coarser strands of basichromatin appear to be 

 suspended. 



Palceolithic: Belonging to the Old-Stone Age, which corres- 

 ponds to the latter half of the Glacial or Pleistocene epoch. 

 It is alleged to be the second period of prehistoric man 

 (following the Eolithic) and is characterized by imple- 

 ments of unpolished stone shaped from flint by the chip- 

 ping off of flakes of the latter substance. 



Palceontology : The science of fossil organisms. 



Palceozoic: A term applied to the second group of fossili- 

 ferous rocks, following the earliest, or Proterozoic, group, 

 and preceding the Mesozoic group. It comprises the Cam- 

 brian, Ordovician, Devonian, Silurian, and Carboniferous 

 systems, and its sediments are the first that contain well- 

 preserved fossils. 



Parasitism: A condition in which one organism (the para- 

 site) residing in, or upon, another species of organism 

 (the host) lives at its expense, the relation being detri- 

 mental to the latter. 



Parthenogenesis: The production of offspring from unfer- 

 tilized eggs. 



Phenotype: The sum-total of external characters by whose 

 enumeration an organism is described — the somatic or ex- 

 pressed characters of an organism (or group of organisms) 

 as distinguished from those that are merely potential in 

 the germ cells. 



Phylogeny: Developmental history of the race, the hypo- 

 thetical evolutionary history of the race, in contradis- 

 tinction to the embryological development of the individual 

 (ontogeny). 



