MUSEUM OF COMPARATIVE ZOOLOGY. 133 



Klaatsch says concerning them (p. 129): " Untcrsucht man einc 

 Schuppe des jungon Lcpidosteus in getrocknotcm Zustando, nach Isola- 

 tion mit verdiinntcr Kalilaugc, so findct man in ihr sclir zahlreiche zu 

 ilu-er Obertlache parallel vcrlaufende ll()lirchen. Dasselbc gilt von 

 den sonkrccht anfsteigenden Faserbiindeln. Die RiJhrchen, welche sic 

 in getrochnetcm Zustande hinterlassen, sind von Williamson bci dor 

 crwachsencn Schuppe als ' tubes lepidines ' bezoichnet wordcn." 



As may be seen in Figure 15 (Plate 11. ), the greater number of these 

 " tubes " have an oblique direction ; none ai*e exactly parallel to the 

 surface, though the onps 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 considei'able 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, 

 diff"ering 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 naiTow 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, howevei', 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 



