30 MAMMARY APPARATUS OF THE MAMMALIA 



of the sweat gland buds present in the pre- 

 ceding stage. Now, however, on the hair 

 follicles of the primary-primordia, small gland 

 buds appear (Fig. 12b, dr), exactly like the 

 sweat-gland buds of Stage 51 (Fig. 12a, sdr). 



Passing on to the next stage (Stage 52, 

 Fig. 13a), we observe still further, and, indeed. 



Fig. 13a. — Echidna: Transverse Section through 

 THE Incubatorial Area OF Semon's Embryo, 

 Stage 52. 



Dr, Gland area ; dr, sweat gland ; Am, skin-musele. 



more marked, progress. The striking feature 



is the very great development of the gland buds 



on the hair follicles of the primary-primordia, 



as compared with the sweat glands of the 



surrounding skin (Fig. 13a, dr)* Finally, in 



* It should be noted that the piece of skin of which 

 Fig. 13a represents a section was much wrinkled ; hence 

 the excessive convexity of the incubatorial area in this 

 figure, which does not correspond to the natural conditions. 



