186 EDWARD B. POULTON. 
Maurer denies to mammals—a periodical shedding of the 
stratum corneum (hair) preceded by the formation of a new 
stratum corneum (new hair) below. The succession of hairs is, 
in fact, the one exception to the gradual wearing off of the 
superficial corneal cells in mammals which is so important a 
difference between them and reptiles. 
Although quite accepting Max Weber’s explanation of the 
scales of Manis, I should agree with Romer in thinking it 
more probable that they are homoplastic rather than homogenic 
with reptilian scales. We must remember that the tongue of 
mammals possesses in its papillz structures quite as comparable, 
except as to situation, with the scales of reptiles as are those of 
Manis; while protection, attrition, or any other advantage which 
can be secured by a papilliform upgrowth from the surface, is 
obtained so simply that it seems unnecessary to explain it by 
genetic relationship. 
My objection chiefly turns, however, on the conclusions forced 
upon me by the study of Ornithorhynchus; for if hairs are 
modified scales and homologues of feathers, it is very unlikely 
that the scales of Manis can be the same. Romer and Emery 
both show hairs developing on the scales of Dasypus, while 
they also prove that these scales are homologous with those of 
Manis. 
Both feather and hair point to some ancestral scale which is 
very different from that now found in reptiles and in Manis. 
I believe that some of the features of this primitive structure 
can be reconstructed with a fair degree of probability. 
Inasmuch as I have argued that the hair of Ornithorhynchus, 
developed in an open pit, was in some ancestral phase formed 
upon the surface, it is legitimate to regard it as a superficially 
placed structure, and then to inquire whether new homologies 
or discrepancies between it and feathers or scales, are thus 
revealed. 
Woodcut fig. 1 is a diagrammatic rendering of a longitudinal 
section of the developing shield of a large hair in Ornithorhyn- 
chus, while woodcut fig. 2 represents its appearance if it were 
formed at the surface instead of ina pit. The wall of the pit, 
