532 



Comparative Morphology of Chordates 



Fig. 414. Olfactory region of hen. (A) Transverse section. (B) Longitudinal 

 section, (c) Middle concha; (ch) choana; (i) inferior (anterior) concha; (o) connec- 

 tion of air-cavity of head; (p) septum of nose; (s) superior concha. (After Gegen- 

 baur. Courtesy, Kingsley: ''Comparative Anatomy of Vertebrates," Philadelphia, 

 The Blakiston Company.) 



veloped and functional. A copulatory organ (penis) of the reptilian 

 type is present only in ostriches, ducks, geese, and a few other birds. 

 In the female embryo paired ovaries and oviducts are formed, but 

 usually only those on the left side develop to functional maturity 

 (Fig. 413). The right ovary and duct may persist in a rudimentary 

 condition or may disappear. This reduction of a paired to a unilateral 

 system is clearly related to the fact that birds' eggs are of such enor- 

 mous size relative to the diameter of the body that they must mature 

 and pass out in single file. 



Nervous Organs 



Some of the nervous organs of birds are more elaborately developed 

 than the corresponding organs of reptiles. On the whole, however, the 

 avian nervous system and the type of behavior which it mediates con- 

 form to the reptilian pattern and show little approach toward the 

 mammalian. 



The structure of the olfactory organ indicates that the sense of 

 smell plays a secondary part in the life of the bird as compared to sight 

 and hearing. The nasal cavities are relatively small. From the outer 

 wall of each cavity three conchae, or "turbinate," project into its 

 interior (Fig. 414), in contrast to the single concha of reptiles. This 

 increase of nasal surface, however, is not attended by corresponding 

 increase of olfactory surface because (in the few birds which have been 

 examined in this particular) the distribution of the olfactory sensory 

 cells is restricted almost or entirely to the posterior concha. The organ 

 of Jacobson is quite lacking in adult birds, but rudiments of it have 

 been observed in embryos. 



