HAIRS OF MONOTREMES AND MARSUPIALS. 583 



to that which takes place in other mammals, and is in the form 

 of a solid epidermic downgrowth. 



(2) The dermic layer takes at first no share in the develop- 

 ment. 



(3) The lower end of the follicle forms at first a flat 

 obliquely slanting plate, indicating possibly a primitive bilateral 

 symmetry in the structure from which the hair is originally 

 derived. 



(4) The plate, by ingrowth of the dermic layer, is transformed 

 into a radially symmetrical bulb moulded on the dermic papilla, 

 this radially symmetrical bulb being formed before the deve- 

 lopment of the hair itself takes place. 



(5) The hair is formed as an upgrowth from the bulb within 

 the solid follicle, up which it pushes its way just as in other 

 mammals^ and it is not developed in a tube open to the 

 exterior. 



(6) The inner root-sheath is developed as a modification of 

 the walls of the follicle, and subsequently becomes transformed 

 into a corneous network surrounding the growing hair. The 

 development of the inner root-sheath is fundamentally similar 

 in large and small hairs. 



(7) There is no relationship between the inner root-sheath 

 of a hair and the appendicular part of a feather. 



(8) The medulla of the hair is formed primarily as a solid 

 upgrowth of the cells which are continuous with those of the 

 stratum Malpighii of the epidermis. 



(9) The cuticle of the inner root-sheath is directly con- 

 tinuous with the cuticle of the hair. 



(10) There is no real distinction of the inner root-sheath into 

 Huxley^s and Henle's layer. 



(11) The larger size of the dermic bulb in the large hairs of 

 Ornithorhynchus, and in the spines of Echidna, is a secondary 

 feature of no phylogenetic importance. 



(12) In all essential respects the development of the hairs 

 in Monotremes is precisely similar to that of other mammals. 



