THE LIVING BIRD 



39 



sionally persist (e.g. various pigeons and hawks) 

 and may actually be functional in some individuals. 

 Unlike most mammals, the testes are retained in the 

 body cavity in birds, lying in close juxtaposition to 

 the adrenals and kidneys. They are very small 



Fig. 7. Part of Section of Testis and Ovary of Junco 



A: part of transverse section of spring testis of Junco, Junco 

 hyemalis (diagrammatic). Int, connective and interstitial tissue; 

 Sem, seminiferous tubules, containing bundles of spermatozoa; 

 Tu, tunica albuginea. B: part of section of ovary of Junco 

 (semi-diagrammatic). Fo, follicle and theca; G. Ep, germinal epi- 

 thelium; Ov, Ova; St, stroma of comnective and interstitial tissue, 

 vessels, etc. 



during the winter and relatively enormous in 

 spring. The greatest contrast in seasonal variation 

 occurs in the migratory species of the northern 

 hemisphere, in which the organs may weigh 1500 

 times as much during the breeding season as they 



