W-chromosomes. — The sex chromosomes in moths, caddis 

 flies, birds and certain fishes. In these types the male has two 

 similar heterosomes (ZZ) and the female has two dissimilar 

 one (ZW). In some cases the female is Z only, with no W 

 homologue. 



Waagen, Mutations of. — Discontinuous changes of small or 

 moderate extent ; particularly used of different forms of fossils 

 of the same lineage but belonging to different horizons. 



Wagner's Separation Theory. — See Separation Theory, 

 Wagner's. 



Warning Coloration. — Conspicuous coloration (especially 

 red) of obnoxious organisms, particularly insects. 



Weber, Organ of. — The uterus masculinus; a small structure 

 lying between the ejaculatory ducts of the male and homolo- 

 gous with the uterus of the female. 



Weissmannism. — Essentially a theory of complete continuity 

 of germ-plasm from generation to generation, this remaining 

 entirely distinct from somatoplasm. 



Wings. — The lateral petals of a papilionaceous flower. 



Wright's Coefficient. — See under Inbreeding Coefficient, 

 Appendix 1. 



Wright, Sewall, Effect. — Non-adaptive differentiation into 

 different types due to "drift" (g.z'.) followed by random fixa- 

 tion in small isolated populations. 



