3 88 



THE HUMAN SPECIES 



and genital organs, a single body and head (Plate IV., fig. d), 

 or the so-called " Janus-head " is produced. In this monster 

 the lower part of the body is double, and the two heads, necks 

 and breasts are conjoined. Lastly, a completely double body 

 may occur and the heads only be conjoined either by the 

 temples, occiput or forehead. When division begins from 

 both ends of the embryo, the monster often lives and is seen 

 in exhibitions. They are united only by the thorax or abdo- 

 men (Plate IV:, fig. b). The union may extend to the neck 

 and jaw ; in other cases there is a single backbone; finally, 

 there are cases in which as a result of cell-division, a stunted 



FIG. 198. Supernumerary milk glands. C, in a Japanese female ; D, in a Baden 



soldier. 



individual incapable of separate existence is attached to the 

 epigastrium of another, or is enclosed in his abdominal cavity. 



Calves and other domestic animals with two separate heads, 

 two faces, " Janus-heads," limbs growing out of their backs and 

 similar double monsters are not infrequent. They also occur 

 in wild animals. Hunter and others have observed lizards 

 with two tails and Lereboullet has carefully studied fifteen 

 cases of fishes in which the gradual union of two previously 

 separate heads has given rise to a double-headed monster. 1 



(d} Excessive development of hair on the face or body 

 combined with poor development of the teeth is a rare 



1 Darwin, loc. cit., iv., p. 386. 





