90 THE MAMMALIA. 



mammary glands as very strange and but little 

 pleasant one, we would remind of the case of the 

 pigeons. Pigeons do not indeed possess glands 

 on the outer skin, but have glands developed in 

 their crops which provide the young with food ; 

 whereas in the other birds we find at most only 

 secretions for softening the food and preparing it 

 for digestion. 



Owing to the fundamental importance of the 

 mammary glands, we must enter somewhat more 

 fully upon the subject here, while discussing the 

 lowest known forms of Mammals. The simplest 

 arrangement is that of the Duck-mole, such as was 

 perhaps inherited from unknown ancestors, but 

 which probably also represent a stage of reversion. 

 It is different with the Echidnas, porcupine ant- 

 eaters. We here find the perforated glandular 

 patch lying somewhat deeper and surrounded by a 

 circular wall of skin. In this so-called mammary 

 pouch the immaturely-born offspring finds admis- 

 sion and protection, and by sucking forms for itself 

 probably a temporary pointed teat. The most 

 important matter is that the formation of the teat 

 or nipple begins in all the other Mammals and in 

 Man with the indications of this kind of mammary 

 pouch. The form and more delicate structure of 



