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THE AMERICAN NATURALIST [Vol. XLVII 



quite similar somatically, the only difference being that 

 the asymmetry present occurred on opposite sides in the 

 two animals. In the older boar the right nipple of the 

 second pair was not developed, and in the younger boar 

 the left nipple of the same pair was suppressed. 



L n. m. 



The Mamma Pattern. — What may be termed the "nor- 

 mal" mammae pattern consists in the occurrence along 

 the ventral side of regularly placed pairs. The first pair 

 lies just behind the junction of the ribs with the sternum. 

 The last pair is inguinal in position, and its members lie 

 close together near the median plane. The intermediate 

 pairs are spaced about equally between, although a 

 slightly greater distance separates the last two pairs. In 

 the male with ten mammae (five pairs), the sheath open- 

 ing lies between the second and third pairs, while the 

 fourth pair is about the same relative distance to the rear 

 of the third. In the female the nipples are similarly 

 placed, but less readily located in a definite manner, be- 

 cause of the absence of the sheath. 



It has been assumed by some writers that the paired 

 mammae bear a relation to the metameric structure of the 



