Professor Owen's Teleology of the Skeleton of Fishes. 219 



at random over their surface, but regularly arranged, as the seaman 

 knows how ballast should be, in orderly series along the middle and 

 at the sides of the body. The protection against the water-logged 

 timber and stones hurried along their feeding grounds which the 

 sturgeons derive from their scale-armour, renders needless the ossi- 

 fication of the cartilaginous case of the brain or other parts of the 

 endo-skelcton to be kept as light as may be compatible with its elas- 

 tic property and other functions. The sturgeons are further adjusted 

 to their place in the liquid element, and endowed with the power of 

 changing their level, and rising with their defensive load to the sur- 

 face by a large expansive air-bladder. 



These teleological interpretations of the derma) bony plates may 

 give some insight into the habits and conditions of existence of those 

 ganoid and heavily protected placoid fishes which so predominated 

 in the earlier periods of animal life in our planet ; whereas these 

 ganoids and placoids have hitherto been viewed almost exclusively by 

 the light of the analogy of an embryonic " Age of Fishes," or explain- 

 ed by the hypothesis of transmuted Crustacea. Some have gone so 

 far as to affirm, that in all those solid parts that cover and shield the 

 exterior of the body of the sturgeon and analogous fishes, " there is 

 nothing in the least analogous to any part of the internal articulated 

 skeleton of vertebrata," but that '* it is entirely a remnant of the 

 superficial shells of invertebrata," (xxvii., p. 3370 You would 

 hardly suppose, from these exaggerated expressions, that both ganoid 

 and placoid plates are as richly organized and permeated by nutrient 

 vessels as the bones within ; and that they present the same micro- 

 scopic structure as the ossified parts of the endo-skeleton, which they 

 servo to protect. I have proved this with regard to the existing 

 Lepidostensy and the extinct Lepidotus (v., p. 14). Drs Peters and 

 Miiller have shewn the osseous rayed corpuscles in the scales of 

 polypterus and other ganoids. Nay, many of the Ganoid fishes 

 have these modified bony scales articulated in regular series by a 

 kind of gomphosis, like the pegs and sockets by which the tiles of a 

 roof are linked together. The dermal bones which form the cara- 

 pace of the armadillo have the same cellulo-reticulate interior struc- 

 ture as the carpal, tarsal, or other bones of the endo-skeleton not 

 excavated by a medullary cavity. This is well demonstrated in the 

 dermal bones of the great extinct Glyptodons.* 



The great proportion of the primitive cartilage which is retained 

 in the skull of many of the osseous fishes, the salmon and pike, for 

 example, and the greater proportion of the animal to the earthy 

 matter in all the bones, their coarse texture, the radiating fibres of 

 the flat cranial bones, and the general absence of dentated sutures, 



* M. De Blainville, in the '• Generalites Osteologiques,'' prefixed to his great 

 " Osteographie," admits that the structure of the dermal bones has a certain 

 resemblance witli that of true bones ; but errs in stating, '' avec cette difference 

 importante, qu'elle n' e.«<t jamais cellulcuse et reticul^e,*' 4to 1839, p. 12. 



