THE SCALES IN SOME TELEOSTEAN FISH. A7 
horizontal slit-like cavity forms in the interior, the floor of some 
of the larger spaces being raised into a small conical elevation 
projecting upwards into the cavity. In none of my speci- 
mens has this papilla been much more marked than is repre- 
sented in Fig. 3. In the majority, I have been unable to 
detect any such elevation. Whether when present they are 
merely artefacts, or whether they are to be regarded as very 
diminutive homologues of the dermal scale papille of 
Selachians may be open to doubt. If so comparable, it might 
be objected that more than one such elevation ought to be 
found in each cavity. It is possible that this may be only a 
central one, and that more may arise at a little later stage, a 
stage which so far I have not been fortunate enough to meet 
with. 
The limitsof the cavity are sharply defined from the surround- 
ing tissues by the still closer arrangement of the nuclei; this 
is rather more evident on the floorof the space. In the latter 
situation there appears to be a very thin layer immediately 
bounding the cavity, from which nuclei are absent, the 
layer having a homogeneous aspect. The nuclei in con- 
nection with the scale cavities are those of the “ Sclero- 
blasten”’ of Klaatsch, the thin homogeneous layer being the 
first indication of the scale. Nickerson writes (loc. cit., 
p. 121): “ The fact that in Selachians the scale is formed over 
the surface of the papille, while in Ganoids (Lepidostens) 
and in Teleosts it arises in the midst of the mass of cells 
forming the elevation is a fundamental difference not to be 
overlooked.” This account of the development of the Tele- 
ostean scale is evidently drawn from the description given by 
Klaatsch. The description and figures given by the latter of 
the early conditions seen in the trout do not correspond in 
detail with what I have just described in the cod. Here the 
scale, if I have interpreted the appearance aright, arises as an 
apparently homogeneous layer covering the surface of what 
may be regarded as the dermal papillz, precisely comparable 
to the early process of scale formation in the Selachians. 
Jf such be the case, then the ‘‘fundamental difference ” 
