NIPPLE DEVELOPMENT IN SQUIREEL 127 



Moreover, the doubling of the two anterior 

 pairs is only apparent. If we examine sections 



Fig. 45a. 



Fig. 45b. 



Fig. 45c. 



Figs. 45a, 45b, and 45c. — " Sciurus vulgaris." Trans- 

 verse Sections (Diagrammatic) showing Succes- 

 sive Stages of Nipple Development. (Beesslau. ) 



JT, Smaller pectoral nipple primordia shifting medio-ventrally from 

 p, primary-primordia pectoral. 



Fig. 45b shows separation of pectoral nipple primordia at a later stage. 

 Fig. 45c shows a still later stage with p, the larger pectoral nipple 



primordium, and ir, the smaller, as elongated epithelial cylinder 



growing into cutis. 



of successive stages (Figs. 45a, 45b, and 45c), 

 we see that at first the smaller primordia it and a 



