28 MAMMARY APPARATUS OF THE MAMMALIA 



these hair primordia, which are crowded to- 

 gether and are sometimes concentrically 

 arranged, is over 100 for each primary- 

 primordium, so that they are henceforward 

 characterized by an unusual wealth of hairs, in 

 contradistinction to their former baldness. 



The significance of these formations comes 

 out more distinctly still in the following stages, 



^i^ 



Fig. 12a.— Echidna : Transverse Section through 

 THE Incubatorial Area OF Semon's Embryo, 

 Stage 51. 



Dr, Gland area ; ?ia, hair bud ; hm, skin-muscle ; sdr, sweat gland. 



Avhen the hair follicles begin to produce glands. 

 The glandular outgrowths, which appear in 

 the neighbourhood of the primary-primordia, 

 slowly develop into typical sweat glands, the 

 histogenesis of which Eggeliug has described in 

 detail. But the glandular outgrowths which 

 arise from the hair follicles in the region of 

 the primary-primordia develop only in their 

 first stages after the manner of sweat glands, and 



