176 EDWARD B. POULTON. 
outer layer of cornified cells and a deeper layer of granule- 
containing cells, immediately surrounding the feather forecast. 
This sheath, then, that is shed later on, he believes to be the 
same thing as the old “cuticle ;’—instead of a new “cuticle” 
below it, there has been formed the feather. He thus explains 
this feather-sheath in much the same way as the believers in 
the feather-hair theory might explain the inner root-sheath. 
But, he points out, there is no such periodical shedding of the 
stratum corneum in mammals, preceded by the formation of 
definite layers below; there is a gradual transition from the 
deepest layer to the most superficial cells which drop off from 
time to time. 
Having in this way contested the supposed homology be- 
tween hair and feather, he proceeds to elaborate his theory 
as to the homology between a hair and an epidermal sense-organ 
of fish and Amphibia. He believes that there is no essential 
difference between an ‘‘ Endknospe” and a “ Nervenhiigel ;” 
each is essentially a collection of nerve end-cells (which may 
or may not traverse the whole depth of the epidermis) sur- 
rounded by elongate supporting cells, which separate the organ 
from the general epidermis. He describes (1892, @) these 
in various fish from different parts of the body. In the Peren- 
nibranchiate Amphibia and in several Caducibranchiate (e. g. 
Triton) they exist throughout life; while in others (Sala- 
mandra) and in Anura they are present only in the larva. 
In the newt, after the metamorphosis, these sense-organs 
have a definite relationship to the wart-like papille which 
have made their appearance. At the top of the wart, in a cup- 
like depression, lies the sense-organ, which is protected by the 
‘overhanging lips of the cup, formed of horny epidermal cells. 
This removal of the sense-organ from the surface and its loss of 
function are evidently related to terrestrial life, and differ from 
the sinking of this same organ in fishes, where it still retains 
its function. 
In Menopoma, Menobranchus, and Cryptobranchus, 
though aquatic, the sense-organ is similarly removed from 
the surface; this he explains by the suggestion that these 
