58 H. W. MARETT TIMS. 
clupeoids, where the spines are but very feebly developed, 
the scales are readily removed, whereas ctenoid scales are 
the most difficult to separate, and in them the spines are. 
most marked. In this respect the cycloid pattern occupies 
an intermediate position. 
Amongst the species of cod whose scales have been ex- 
amined, those of G. callarias retain the most primitive 
condition, while those of G. minutus seem to be converging 
towards the clupeoid pattern. But both cycloid and clupeoid 
type agree in this fundamental particular—that they both 
arise as anumber of minute scalelets of the placoid 
variety. 
MorpHo.oey. 
It now remains to discuss briefly the morphological bearings 
of this interpretation of the scale structure. Hitherto the 
Teleostean scale has always been regarded as a morphological 
entity. This will be evident from the following quotation 
from the important memoir of Klaatsch (12). On page 174 
he writes: ‘‘ Die Teleostierschuppe entspricht der Basalplatte 
der Placoidschuppe”; and again: “Jede Teliostierschuppe 
einer Placoidschuppe entspricht.” 
From a consideration of the facts set forth in this paper one 
is led to the opposite conclusion, namely, that the scale of the 
Teleostei is a compound structure, the morphological unit 
being the individual scalelet, each of which is the homologue 
of a single placoid scale of the Selachians. When I first 
enunciated this view at Belfast I was unaware that a similar 
interpretation had been placed upon the Ganoid scale by 
O. Hertwig (6), an interpretation which both Klaatsch and 
Nickerson refuse to accept. This view is, I believe, quite 
new in regard to the Teleosteans, and the fact that a similar 
interpretation has been placed upon the ganoid scale by so 
high an authority as Hertwig is a fact of the utmost value in 
its support. 
The union of a number of placoid scales upon a single 
fibrous basis would lead to the formation of a teleostean 
