THE SCALES IN SOME TELEOSTEAN FISH. 61 
it follows that many of the deductions of previous authors 
from the evidence of the scales alone will necessarily have to 
be modified. 
As above stated, Hertwig has made a similar suggestion as 
to the morphology of the ganoid scale. ‘To this Klaatsch 
objects owing to the great number and indefinite arrange- 
ment of the spines in the Selachians. Neither of these 
objections appears of much weight, since the number of scales 
must have been very considerably greater in the larger and 
more primitive Selachians, and with a reduction in body size 
the spines would tend to be more crowded, but not of necessity 
in the first instance to have undergone any very great 
numerical reduction. Secondly, the tendency to a fixation of 
the scales in situ upon a fibrous basis would impede the 
movements of the body. In order that this might be pre- 
vented as much as possible without impairing their other exo- 
skeletal functions the scales have assumed a definite shape 
which has consequently interfered with the regular linear 
arrangement of the scalelets. If the disposition of the latter 
be examined, not from the point of view of excentrically 
arranged lines, it will be seen that those on the lateral fields 
still preserve a very fairly definite antero-posterior series, 
while in the anterior and posterior areas this plan is but little 
disturbed. 
I pass to a consideration of the points involved in the 
account of the early stages of the development. It has been 
seen that the teleostean scale arises and remains throughout 
its existence as a dermal structure. This at first sight 
appears to present a difficulty in homologising the scalelet 
with a placoid scale or with the scales of Lepidosteus. In 
the development of the two last-mentioned the greater part 
of the spine is dermal; it is only the enamel tip which is 
epidermal in origin. ‘his in Lepidosteus is only sub- 
sequently added when the dermal spine has reached the lower 
boundary of the epidermis. It is also at this time and from 
the same source that the scale receives its layer of ganoin. 
In the Teleosteans the spines are so much reduced in size 
