MUSEUM OF COMPARATIVE ZOOLOGY. 133 
-Klaatsch says concerning them (p. 129): “ Untersucht man eine 
Schuppe des jungen Lepidostens in getrocknetem Zustande, nach Isola- 
tion mit verdiinnter Kalilauge, so findet man in ihr sehr zahlreiche zu 
ihrer Oberfliche parallel verlaufende Robrchen. Dasselbe gilt von 
den senkrecht aufsteigenden Faserbiindeln. Die Roéhrchen, welche sie 
in getrochnetem Zustande hinterlassen, sind von Williamson bei der 
erwachsenen Schuppe als ‘tubes lepidines’ bezeichnet worden.” 
As may be seen in Figure 15 (Plate II.), the greater number of these 
“tubes” have an oblique direction; none are exactly parallel to the 
surface, though the ones near the ends of the section are nearly so, and 
only a small part are vertical. Thus it is evident that their courses are 
not the same as those of the fibres of dermis which has not undergone 
calcification, neither do they agree with Klaatsch’s statement concerning 
them. It is also noticeable that they do not have the same direction as 
the dentinal tubules among which they lie, but that the two often cross 
at considerable angles. Klaatsch does not account for this, neither am I 
confident that I can explain the causes of the differences in direction to 
which I have called attention; but it would seem to be due to the 
odontoblast cells—in common with a part of the other scleroblasts — 
migrating before the advancing line of calcification in a direction per- 
pendicular to the surface of the scale adjacent to them, such migra- 
tion being however independent of the course of the fibres among which 
they lie. 
I find that the small scales from the under side of the lower jaw agree 
with the description and figures of Hertwig (’79, pp. 2, 3, Taf. I. Figg. 
1-5). They closely resemble the larger scales in all essential respects, 
differing from them chiefly in size and in having the form unmodified 
by the proximity of adjacent scales. They are composed of a basal 
bony plate, which is not destroyed by acid, of which the central part is 
covered by a layer of ganoin, soluble in acid, about which there remains 
a narrow marginal area not covered by the ganoin, but bearing one or a 
few spines. The number of the spines, upon which Hertwig laid empha- 
sis, is, however, as has been stated concerning the larger scales, entirely 
indefinite, and can be of no morphological importance. The scales 
described by Hertwig as having one spine owe this condition doubtless 
to the others having been lost, not to the scale having been developed 
as the basal plate of that single spine, as is the case in the placoid 
scale. Such scales cannot therefore be considered as the complete 
homologues of the placoid scales of Selachians. 
Mark (’90, p. 11) has described the act of swallowing in the young 
