100 ZOOLOGY DIRE CTIONS 



ing resemble the adult except for the lack of certain adult 

 organs. The young of insects having incomplete metamor- 

 phosis. 



Optical section — The reconstruction of what a slice through an 

 object would look like. 



Oral surface — The surface on which the mouth is located. 



Organ — A group of cells or tissues which together perform some 

 specific function. 



Parthenogenesis — Reproduction through unfertilized eggs. 



Parthenogenetic colony — A colony carrying germ cells which de- 

 velop without fertilization. 



Pellicle — A thin, non-living cell wall covering the body of most 

 Protozoa. 



Plane of symmetry — Any plane which passed through an object 

 divides the object into two parts of corresponding size and 

 form. 



Posterior — At or toward the hinder end of the body. 



Prolegs — Larval legs, without joints, upon the abdomen of some 

 insect larvae. 



Pseudopodium — Temporary protoplasmic process thrust out 

 from membraneless cells. 



Pupa — The inactive stage between the larva and adult of insects 

 having a complete metamorphosis. 



Radially symmetrical — Having the parts of the body repeated 

 around a central axis like the spokes of a wheel. 



Rayed fin — A fin, the membrane of which is supported by a 

 series of spines or 'rays.' 



Right — (See definition of left.) 



Regeneration — The power of an organism to replace a lost part. 



