128 BULLETIN OF THE 
The scleroblasts overlying the scale about the bases of the spines do 
not cease their secretive activity when the spines are completed, but 
their secretion continues to be employed gradually to thicken the scale 
by additions to its upper surface. The amount of material so added 
is very little in the central part of the scale, but toward the margins, 
where growth is still taking place, and where the greater number of 
spines are formed, it is considerable (Plate II. Fig. 13). This results in 
the basal ends of the spines being surrounded and incorporated in the 
outer layers of the scale (Plate IV. Figs. 24, 25). These outer layers 
also contain enclosed cells, and are composed of exactly the same mate- 
rial as the layers immediately underlying them. 
It is this outer part of the scale which Klaatsch believes to be the 
enamel layer of Hertwig and other authors, and which he calls gano. 
He says (p. 141): “Sie [die Ganoinschicht] entsteht im Anschluss an 
die Zahnbildung auf der Schuppe; sie ist eine direct Fortsetzung des 
Zahnbeins der kleinen Schuppenziihne.” He also says (p. 132) : “ Die 
Substanz der Ganoinschicht stimmt in ihrer homogenen Beschaffenheit 
mit dem Dentin der Zähnchen überein.” 
In this I believe that Klaatsch is in error. It is inconceivable to me 
that any one who had seen ground sections of the ganoin under the 
microscope could for a moment confound with it the dentine of the 
spines. Moreover the figure of ganoin given by Klaatsch (Tafel VII. 
Fig. 6) represents a condition quite different in appearance from that 
presented by the true ganoin. Furthermore, as shown by the table 
already given (page 117), I found no trace of the ganoin layer on the 
scales of a fish 289 mm. long while the fish from which Klaatsch's mate- 
rial came was only 180 mm. long. Reissner (59, p. 260) says concerning 
the spines “ihre Insertionsstellen unmittelbar unter dem Schmelz lie- 
gen." The presence in this outer layer of enclosed osteoblasts, which are 
absent from the layer described by Reissner and Hertwig, the fact that 
it is not destroyed by acid, and its optical properties, all give convincing 
proof that the material secreted “im Anschluss an die Zahnbildung 
auf der Schuppe” is not the layer described by Hertwig and others 
as enamel. If then, as I believe, Klaatsch did not sce the layer in 
question, his claim in regard to its origin can have no weight, and the 
question of its source remains where Hertwig loft it.! 
1 Tt is only fair to state, however, that both the 17.5 em. and the 19 em. gar- 
pikes which I studied were killed in acids, so that I haveno undecalcified material 
of the same size as that which Klaatsch studied, for a perfect control of his state- 
ment about the ganoin layer. 
