NATURE OF PRIMARY-PRIMOEDIA 37 



retrograde metamorphosis during the embryonic 

 development. 



If we proceed to inquire as to the nature of 

 those organs of which the primary-primordia 

 may be regarded as the vestiges, it is permissible 

 to suppose that they functioned in some way in 

 relation to the care of the offspring by the 

 parent, and that thus, long before the appear- 

 ance of the incubatorium and mammary glands, 

 through these organs there existed some con- 

 nection between the young and the abdomen of 

 the parent animal. 



Such considerations led me to regard these 

 formations as organs with which the oviparous 

 ancestors of the recent Mammalia hatched 

 their eggs — i.e., organs analogous in nature to 

 the so-called Brutflecken or brooding-spots, 

 such as are seen in many birds , These brooding- 

 spots lie as paired or unpaired formations on 

 the ventral side of the abdomen, and are fully 

 developed sometimes in the female, sometimes 

 in both sexes, in isolated cases only in the male. 



According to the exact investigations of 

 Barkow in 1829, these spots are already 

 clearly differentiated in the young and are 

 distinguished as areas free from cutaneous 



