278 Dr L. Mandl's Eesearches on the 



this observation may be repeated on a nuiltitudc of other scales (for ex- 

 ample, the membranous ones), \vc will find the eanal now transformed in- 

 to a true furrow. The upper wall is entirely wanting ; the lower wall, 

 or rather the bottom, is formed only by the inferior layer of the scale 

 (fig. 7, a), which constitutes the marginal space by its prolongation. 

 There are no lateral walls properly so called, they are only formed by the 

 interruption of the superior layer. 



In this case, therefore, it is not a hollow tube, as in the preceding ex- 

 amples, which traverses the scale, but it is simply the absence of the 

 superior layer which constitutes the longitudinal line. By glancing at 

 the figures from 4 to 7, we have the difTerent forms under our e\"e, from 

 a simple furrow to a tube almost entirely closed, or pierced only in seve- 

 ral places. 



This last example denionstrat s that the canals, or rather the tubes 

 by which more or less osseoxis scales are traversed, are of the same na- 

 ture as the longitudinal lines of which we have formerly spoken. 



In fact, if we examine the plates which cover the surface o^ Syngnathus , 

 we shall find them pervaded by tubes entirely closed, in no instance des- 

 titute of walls, insulated towards the margin, and anastomosing towards 

 the centre of the scale ; or enclosed, towards the bottom, between the 

 anastomoses of these tubes, forming numerous insulated compartments. 



This tissue docs not present an osseous structure ; but in scales cha- 

 racterized by this latter organization, such as that of the Scinci (pi. III. 

 fig. 8), the longitudinal lines form tubes perfectly closed and rounded as 

 in the preceding example. The ground exhibits osseous corpuscles with 

 small canals attached to them (fig. 8, b). All osseous scales, plates, &c. 

 display nearly the same form, a circumstance which has caused us to limit 

 our observations to the scales of the Acanthopterj-gians and Malacoptery- 

 gians, the scales of other fishes, as far as we have had an opportunity of 

 observing them, possessing only closed tubes traversing an osseous tissue. 



These tubes sometimes rise above the surface of the scale and form 

 true spines, as in Gadus euxinus, skate, &c. They then appear to be com- 

 posed of a fibrous tissue, as indicated by the longitudinal lines which 

 run from their base towards the summit. 



By casting our eye over these different forms presented to us in the study 

 of the scales mentioned, and which might be further increased by many 

 examples of intermediate degrees, it seems to us proved that the longitu- 

 dinal lines appear under all forms, from that of a simple furrow, to that 

 of a closed and hollow tube, which latter is found filled in osseous scales. 

 But in the majority of cases, this tube is hollow, and, whether it be closed 

 or open, it may always be considered as a can.il. Elementary anatomy 

 shews us that osseous tissues are at first cartilngiuous and traversed hy 

 vessels, hollow tubes, which, at a later period, become filled up. Thus, 

 the tubes even of osseous scales (pi. III. fig. 8), take their place by the 

 side of the others, if we examine them during their development, before 

 they have attained the highest stage of their organization. 



The lines in question, then, present us in all their forms, with a series 



