and on Scales in Mammals. 9 



of other species of Macropus, which use their tails in a pre- 

 cisely similar fashion, scales are wanting. What advantage 

 does the short tail of Peramehs doreyanus derive from its 

 Avell-developed coat of scales, while the similarly constituted 

 tails of Perameles Ounni and P. ohesida are scaleless ? The 

 species of Phalanger with a typical prehensile tail are without 

 a coat of scales, and the same applies to the prehensile tails 

 of monkeys. The arboreal Sciuridge, too, have scaleless tails. 

 The large rows of scales on the ventral surface of the root of 

 the tail of the Anomaluridte are a specialization and a further 

 development from, small scales, which cover the entire tail. 



Moreover, what is the nature of the adaptation that causes 

 the extremities of many Marsupialia, Rodentia, and especially 

 Insectivora to bear scales or indications of such ? 



The foregoing examples clearly illustrate the irregularity 

 of the occurrence of scales even in the case of most closely 

 allied species, as well as their independence of the mode of 

 life of the animals. They become intelligible when we con- 

 sider them from the point of view that scales are rudimentary 

 structures, which have persisted in different degrees or in 

 ])art already disappeared, and only in altogether isolated 

 cases underwent further development in a specialized form 

 (Manidaj, Dasypodida;, Casto?-, Anomalurus). Romer, on 

 the contrary, considers that the scales " are secondary pheno- 

 mena of adaptation, which were acquired by true hair-bearing 

 animals, since they were more advantageous to them for their 

 mode of life, e. g. for the tail as a prehensile and supporting 

 organ, than the less firm coat of hair." 



On the other hand, Romer justly ascribes to me the view, 

 that I held it to be improbable that the scales had developed 

 as structures entirely new and without an inherited basis. 

 In opposition to this Romer observes, " The inherited basis 

 is, however, suj)plied in the wonderful capacity for ditferen- 

 tiation possessed by the skin, which is indeed to be found in 

 all groups of animals." What the respected author meant 

 to convey by this somewhat formal paraphrase of the fact 

 that the mammalian integument can actually produce scales, 

 I was unable to quite understand. I found the greater diffi- 

 culty in doing so since he goes on to state that " the scale- 

 like coverings of Mammals, which develop in consequence of 

 a capacity of the integument inherited from the Reptiles, and 

 so to a certain extent are to be regarded as a case of ' throwing- 

 back,' justify the conclusion that such a covering was 

 formerly of general occurrence and clothed the entire body, or 

 at least the dorsal parts thereof." 



How great the agreement between us is may be gathered 



