GLOSSARY OF EMBRYOLOGICAL TERMS 297 



Pole, Vegetal — region of egg opposite animal pole; region of lowest meta- 

 bolic rate; pole with greater density of yolk in telolecithal eggs; gen- 

 erally endoderm-forming region of egg. 



Polyembryony — production of several separate individuals from one egg 

 by an early separation of its blastomeres; possible origin of some 

 identical twins. 



Polyploid — possessing a multiple number of chromosomes, such as triploid 

 (three times the haploid number), tetraploid (four times the haploid 

 number), etc. Alwavs more than the normal diploid of the typical 

 zygote. 



Polyspermy — insemination of an egg with more than a single sperm, 

 occurring generally in chick egg, although but a single sperm nucleus 

 is functional, in syngamy. 



Post-Ana! Gut — posteriorly projecting blind pocket of hindgut, that por- 

 tion of hindgut posterior to anal plate or proctodeal plate. (Syn., post- 

 cloacal gut.) 



Post-Reduction — maturation in which equational and reductional divisions 

 occur in that order. 



Posterior Tubercle — See Tuberculum posterius. 



Potency, Prospective — sum total of developmental possibilities, the full 

 range of developmental performance of which a given area (or germ) 

 is capable. Not to be confused with competence. 



Preformation — theory that adult is represented in miniature within egg 

 or sperm and that development is simply enlargement. 



Pre-migratory Germ Cell — yolk-laden cells of splanchnopleuric origin 

 which migrate by way of blood vessels to gonad primordia. Believed 

 by some to be precursors of gonad stroma or functional germ cells. 



Pre-Reduction — maturation in which reductional and equational divisions 

 occur in that order. 



Presumptive — expected or predicted outcome of development of a given 

 area (e.g., fate of a part in question) based on previous fate map 

 studies. 



Primary Oocyte — termination of growth phase in maturation of ovum from 

 oogonial stage, prior to any maturational divisions. 



Primary Spermatocyte — stage in spermatogenesis in which division results 

 in secondary spermatocytes; stage beginning with growth of sperma- 

 togonia. 



