10 On the Origin of Hair and on Scales in Mammals. 



from my previous words {I. c. p. 14) : — " I do not maintain that 

 these scales, as they lie before us, are acquired from the 

 Reptiles, but I regard as that which is inherited only the 

 capacity of the caudal integument of Anomalurus to form 

 such scales." And further on (p. 19) : — '^ We had come to 

 the conclusion that the ' scales ' of the Manidaj are structures 

 which are to be derived from the scales of Reptiles. From 

 our statement it will be clearly seen that we do not regard 

 the two organs as completely homologous. The considerable 

 difference between the horny scales of Reptiles and those of 

 the Manidee has indeed already been expressly pointed out. 

 But we really believe that both had a common origin. . . ." 

 When, therefore, Eomer proceeds to declare that we must 

 not, however, forget " that we here have not before us scales 

 in their original form," I cannot apply the admonition to 

 myself, if Romer by an " original " scale means a Reptilian 

 one. .Now, however, comes the difference, for Romer goes on 

 to write — '' but a secondary scale, which has developed anew 

 upon true hair-bearing animals, for that is proved by the 

 embryonic hairs of Manis * and Dasypus, and is traceable to 

 an adaptation of the skin to the mode of life." It is conse- 

 quently assumed by Romer that Mammals, proceeding from 

 scaly Reptiles, lost their coat of scales, developed hairs, and 

 now could obtain scales once more only by adaptation to the 

 mode of life, and therefore as a " secondary new acquisition." 



In my opinion, however, the primitive Mammals, which 

 developed from primitive, scaly, poikilothermic Reptiles, were 

 clothed with scales. Behind these scales small and sparse 

 hairs at first arose. Whether these w^ere developed by modi- 

 fication from smaller scales or proceeded from nerve-end 

 eminences which were situated between the scales I do not 

 venture to decide. 



With the production of the constant body-temperature 

 and of vigorous metabolism, wherein influences of tempera- 

 ture must have been decisive^ the hairy coat acquired a better 

 development, since it protects the body against loss of heat by 

 radiation and conduction. With this the integument had 

 assumed its special Mammalian character, w4iich also expressed 

 itself in the scales, especially in their horny superstructure. 

 Indeed I previously designated the difference between the Rep- 

 tilian and Mammalian scales as one of the kind that belongs to 

 the Reptilian and Mammalian integuments as such. With the 

 increase in the number and size of the hairs, which conse- 



* The embryonic liairs of Mariis only prove that the hairs are formed 

 where they afterwards stand, consequently in always scanty numbers 

 behind the scales. 



