NIPPLES IN RUMINANTS 119 



into regular nipple pouches, but are only more 

 or less imperfectly hollowed out. Then, after 

 the milk-gland buds have appeared at their 

 bases, they gradually become shallower, in 

 order to form the surface of the nipple, whilst 

 the elevation of the nipple is entirely due to 

 the cutis wall. As regards other forms of 

 nipple development in Placentals, it need only 

 be said that we can recognize a series of types 

 in which the knob-shaped primordia contribute 

 less and less to the formation of the nipple 

 surface, and the cutis wall more and more. 

 These types culminate with the nipples of the 

 Ruminants. Here the knob-shaped primordia, 

 except for the primary depression, do not hollow 

 out, and the entire nipple is produced exclusively 

 by the cutis wall. The knob-shaped primordium 

 gives origin to a single mUk-gland bud, and then 

 gradually becomes reduced during the elevation 

 of the nipple. It persists only on the tip of 

 the nipple as the minute area on which the 

 milk duct opens. These facts are quite easily 

 observable, as I myself, as well as a number of 

 recent observers, have ascertained. It is thus 

 inconceivable how the old erroneous views can 

 be repeated again and again in all textbooks. 



