50 H. W. MARETrT TIMS. 
factor is, I believe, of considerable importance in producing 
the modification in shape which the denticles undergo in 
their further development. 
By the continued growth of the scale, the posterior margin 
reaches the surface of the derma, lying between it and the 
superposed epidermis. It is more than probable that this is 
the cause of the tendency of the epidermis to become 
separated. As far as I have observed it, there is no corre- 
sponding elevation of the epidermis, the scale lying altogether 
beneath it. It remains throughout in the scale-pocket 
(Schuppen tasche, Klaatsch), which becomes stretched 
over the superficial surface of the scale, following all the 
irregularities. It is this pocket which mainly acts in retain- 
ing the scale in position. In larger scales—for example, in 
the herring—the pocket becomes still more stretched and 
attenuated, possibly even ruptured, and this would account 
for the ease with which the scales may be detached in the 
Clupeoids. 
STRUCTURE OF THE FULLY-FORMED SCALE. 
I have been unable to find in the literature any adequate 
account of the fully-formed Teleostean scale. ‘They have 
been described as ‘variously sculptured,’ ‘ ringed,” 
“marked with concentric and radiating lines,” ete., but 
all such descriptions are misleading and fail altogether to 
interpret their true structure. From the following account 
it will be seen that the cycloid scale is a complex struc- 
ture. It consists of a fibrous substratum which preserves 
the general form of the scale. Upon the upper surface of 
this are placed a number of calcified plates, or ‘ scalelets” 
as they may be termed. Covering the entire upper surface 
is a very delicate membrane distinct from the thickened 
epidermis which clothes the surface of the body generally, 
and which is in reality the thinly stretched outer wall of 
the scale-pocket above mentioned. The fibrous stratum may 
best be revealed by placing the scale for some minutes in 
