io6 



THE HUMAN SPECIES 



Monotremata. They possess proper milk-secreting glands with 

 orifices but no nipples, these being first found in the marsupials. 

 Now, on the authority of Kolliker and Langer, the mammary 

 glands are developed in the human embryo before the mamma? ; 

 hence Darwin l concludes that the fundamental form from 



which man arose had mammary 

 glands but no nipples. Wieder- 

 sheim - goes still farther, and 

 points out that the double 

 breasts, possessed by man in 

 common with the elephants, 

 sirenia, edentata, bats, beavers, 

 apes and certain semi-apes, have 

 been gradually acquired in the 

 course .of his history. That 

 man's early ancestors were fur- 

 nished with more than one pair 

 of mammae is proved not only 

 by the frequent occurrence of 

 supernumerary mammae in men 

 and women, which are generally 

 regarded as cases of reversion, 3 

 but far more conclusively on ontogenetic grounds, the investi- 

 gations of H. Schmidt, E. Kallius and H. Strahl having revealed 

 the fact that the bilateral ventral lactatory line (Milchlinie) 

 plainly visible in the embryos of other mammals is also to be 

 seen in the human embryo of 1 5 mm. long, only here it is not 

 quite so strictly bilateral and symmetrical. In an embryo of 

 this size, besides the mammary glands proper, which are visible 

 to the naked eye, eight smaller modifications of the epithelium 

 may be seen on either side. The investigations of E. Bresslau 4 

 are also of great interest. Bresslau traces the above-mentionea 

 line to the marsupial pouch, which in its turn is derived from 

 the mammary sacs of the Monotremata, those small bag-like 

 depressions in the epidermis each of which encloses a nipple. 



1 Darwin, loc. cit., v., p. 212. 2 Wiedersheim, loc. cit., p. 23. 



:i Bonnet, "Die Mamma-Organe im Lichte der Ontogenie und Phylogenie," 

 Anat. Ergcbnisse, 1892, pp. 604-58. 

 4 Wiedersheim, loc. cit., p. 25. 



FIG. 56. Trunk of a girl of Vista. 

 (Hartmann.) 



