GLOSSARY 371 



Phylum: A term used in classification to denote any primary 



group of the plant or animal kingdom. 

 Plantigrade: Walking on the whole sole of the foot, like 



bears. 

 Plastids: Permanent organelles or living components of the 



cellular cytoplasm, e.g., chloroplasts, leucoplasts, etc. 

 Pleistocene: The lower series of the Quaternary system of 



fossiliferous rocks. It corresponds to the so-called Glacial 



epoch, and extends from the close of the Tertiary period 



(system) to the dawn of the Recent or Historical epoch. 

 Polar Cell: A synonym for polar body, or policyte. The 



polar bodies are minute abortive cells given off by the 



egg undergoing meiosis. Into them are shunted the 



chromosomes which the egg discards in its' process of 



nuclear reduction (maturation). 

 Prceformation: Theory that the egg contains a complete 



miniature of the organism into which it develops. 

 Prehension: Grasping, catching hold. 

 Progression: Advancing movement, locomotion. 

 Pro-simim: The lemurs as distinguished from genuine apes 



(Simiae). 

 Protista: Animals or plants which are normally unicellular 



and which when multicellular show no differentiation into 



tissues — the Protozoans and Protophytes. 

 Protoplasm: Living matter. 



Receptor: An organ specialized to receive stimuli, e.g., a 

 sense-organ. 



Sedimentary: A term applied to rocks which originated as 

 sediments deposited under water. 



Serum: Watery portion of the blood, the plasma. 



Somatic Cells: Vegetative cells not especially set aside by 

 the organism for reproductive purposes, e.g., tissue-cells'. 



Somite: One of the uniform segments of the longitudinal 

 series into which a metameric organism (such as an earth- 

 worm) is partitioned. 



Spermatist: An old term applied to one who held that the 

 animal embryo was produced entirely by the male parent, 



