62 H. W. MARETT 'TIMS. 
that they do not, during the period of their growth and 
development, attain that superficial position. Consequently, 
neither enamel nor ganoin is formed upon them. This does 
not offer to my mind any serious obstacle in establishing their 
homology ; it is simply that they have not reached to the 
same level, and as a consequence the epidermis has had no 
opportunity of sharing in their formation. This view finds 
support in the opinion to which Nickerson inclines, that the 
enamel is not secreted in Lepidosteus until at Jeast a part of 
the spine has been formed. The development of the tele- 
ostean scale shows that it is entirely a dermal structure; and 
regarding the line of demarcation between the dermis 
and epidermis as Huxley’s protomorphic layer, it follows 
that the entire scale must be regarded as of enderonic origin, 
and that the scale is covered throughout its existence by the 
superficial layer of the scale-pocket, which is also enderonic. 
The successively formed layers of the fibrous substratum are 
added to the deeper surface, the direction of growth being 
from without inwards, precisely in the direction which Huxley 
regarded as being indicative of the growth of enderonic 
tissues. The calcified layer, the first part of the scale to be 
formed, does not increase in thickness after being once 
formed, there being merely an increase in size and alteration 
in pattern of the individual scalelet. As to the presence of 
the true ganoin in the teleostean scale I cannot but agree 
with Nickerson in thinking that Klaatsch is in error, and that 
in the scales of the Gadidz no such material is present. 
Huxley (11), following Williamson, regards fish-scales as 
“essentially tegumentary teeth,’ and of this there can be 
but little doubt, but the further conclusion of these writers, 
that the scales are formed by a calcareous deposit in a deep 
layer of the ecderon, I think erroneous. Presumably what 
they interpret as the deep layer of the ecderon I have re- 
garded as the superficial nuclear layer of the enderon. It is 
difficult to establish a difference now that the importance of 
the basement membrane is no longer upheld; but from the 
marked difference in the histological characters, and judged 
