BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 179 
of the rat and other mammals, as directly descended from those 
of reptiles, and as remnants of an original scaly covering of 
mammals; the arrangement of hair on the body of these ani- 
mals being dependent upon the scales. He also holds that 
even in scaleless mammals the arrangement of hair retains the 
impress of the original scaly covering. Romer, on the other 
hand, regards the scales as secondarily acquired. These scaly 
mammals are, according to him, descended from hairy mam- 
mals; the epidermis merely retains the power, inherited from 
reptiles, of forming scales, which are thus not directly descended 
from those of reptiles and not strictly homologous with them 
(rather they are homoplastic). 
As to hairs, Romer does not attempt to refer to any other 
epidermal structure as their ancestor, but follows Haacke in 
his suggestion that an explanation of the epidermic down- 
growth of the hair forecast may be found in the fact that the 
scales of reptiles touch or overlap, and between two scales 
there is therefore a depression of the epidermis. Of this he 
says, ‘‘In this epidermal depression I see the spot for the 
origin of the hair, whence the hairs will develop by a cornifica- 
tion of the epithelial cells.” 
LITERATURE. 
1. RetssnER.—‘ Beit. z. Kenntniss d. Haare d. Menschen und d. Saugethiere,’ 
1854. 
2. Gottr.— Zur Morphologie der Haare,” ‘ Arch. f. Mikr. Anat.,’ iv, 1868. 
8. Krerpert.—‘‘ Ueber die Haut d. Reptilien und anderer Wirbelthiere,” 
* Arch. f. Mikr. Anat.,’ xiii, 1877. 
4. StupEr.—“ Beit. z. Entwickelungsgeschichte d. Feder,’’ ‘ Zeit. f. wiss. 
Zool.,’ xxx, 1878. 
5. Davins.—‘‘ Die Entwick. der Feder und ihre Beziehung zu anderen 
Integumentbilden,” ‘Morph. Jahrb.,’ xv, 1889. 
6. Haacxr.— Ueber die Entstehung d. Saugethiere,”’ ‘ Biol. Centralbl.,’ 
vili, 1889. 
7. Lzypic.—(a) “ Integument briinstiger Fische und Amphibien,” ‘ Biol. 
Centralbl.,’ xii, 1892, p. 205. 
8. Leypic.—(d) “Besteht ein Beziehungen zwischen Hautsinnesorgane 
und Haaren ?” ‘Biol. Centralbl.,’ xiii, 1893, p. 359, 
