HEREDITY 



175 



Fig. 108. — Andrian Jeftichjew, the 

 Russian dog man, showing extraor- 

 dinary covRring of hair on the face. 

 (After Wiedersheim.) 



developed in the embryo than in 

 the adult, becoming atropliied 

 with age. Familiar examples 

 are the appendix vermiformis 

 and the unused muscles of the 

 ears in man, the atrophied lung^ 

 pelvis, and limbs of the snake, 

 the air bladder of the fish, the 

 "thumb" (or rather index fin- 

 ger), of the bird, the splint bone 

 of the horse, and the like. 



The anatomist Wiedersheim 

 has recorded 180 vestigial or- 

 gans in man. These structures 

 occur in all the systems of 

 organs, integument, skeleton, 

 muscles, nervous system, sense 

 organs, digestive, respiratory, 



circulatory, and urino-genital systems. Most of these rem- 

 nants of structures are to be found completely developed in 

 other vertebrate groups. Eleven of them are characteristic 

 as functional organs of fishes only, four of ampliibians and 

 reptiles. The fact that structures are vestigial is shown often 



by cases of atavistic de- 

 velopment. 

 Within 



the brain of 

 man, near the optic lobes, 

 is a little spheroid structure 

 scarcely larger than a pea, 

 known as the ''pineal 

 gland" or conarium. It 

 has no evident function, 

 and Descartes once sug- 

 gested that it miglit be the 

 seat of tlie soul. It is 

 larger in the embryo and 

 stin larger in tlie l)rains of 

 some of the lower verte- 

 brates. Recent investiga- 

 tions have shown tliat it 

 is especially developed in 



I'iG. 109. — Pineal eye of lizard, S])licuodun 

 (Jluttcria). (After Baldwin Sin-ncer.) 



