HAIRS OF MONOTREMES AND MARSUPIALS. 581 



structure, and in the other a spiue, that the papilla begins to in- 

 crease in size, and to extend any distance up the shaft. Poulton 

 (p. 183) says, "The great length of the papilla projecting 

 through the bulb into the lower part of the hair is also very 

 significant, suggesting a previous development like that of a 

 scale or feather from the surface of the epidermic covering of 

 a papillary core traversing the structure from base to apex." 



Various authors, and especially Maurer, have insisted upon 

 the fact that the dermic papilla is always developed at a slightly 

 later time than the epidermic forecast. In the case of Marsu- 

 pials, such as Peraraeles, Macropus, Sminthopsis, and Dasyu- 

 roides, we can confirm the conclusions of Maurer. The earliest 

 indication of the hair forecast in these animals has the form 

 of a lengthening and definite arrangement of the elements of 

 the Malpighian layer, the dermic layer at first taking no part 

 whatever in the formation of the structure. In the typical 

 mammalian hair the dermic papilla is never of very large size, 

 and it is only in those cases in which we get special modifica- 

 tions to form spines, &c., that we find, not as a primary but as 

 a secondary feature, that the papilla increases in size and ex- 

 tends some distance up the shaft. The very fact that this 

 development is only found in what is clearly a secondary modi- 

 fication of the hair, which up to the period at which the modi- 

 cation begins to show itself develops in the ordinary way, is 

 sufficient to indicate the fact that in the case of the Mono- 

 tremes the special development in question has no phylogenetic 

 signification of any kind. All that it signifies is simply the 

 fact that, as might be expected to be the case, the larger the 

 hair (or its modification, a spine) becomes, the larger is the 

 dermic papilla. 



It seems probable that the connection between feathers and 

 hairs, if any such thing really exists, is a very remote one, and 

 can only be traced back to some simple form of epidermic, and 

 perhaps scale-like structure, of the former existence of which 

 common ancestral structure we have in hairs a possible indi- 

 cation in the flat plate, which at a very early stage is developed 

 at the base of the follicle in Monotremes (figs. 11, 12, 12 a). 



