Df.crmber 2, 1889.] 



KNOWLEDGE 



25 



and foliage we now burn in our iires as coal. Strange 

 and niicouth must have been many of these old fishes, whose 

 liDilies were encased in a complete coat of plate-armom- 

 unlike that found in any living forms, and consisting of 

 larger or smaller shield-like bones closely united together 

 at their edges. The head, too, in some of these fishes 

 (Fig. 1.) was most remarkable, and looked something like 



Fig. 1. — An Armouued Fish (Cc/i/inlax/iis) of tiik (Ii.d Red 

 Sandstone. 



a flattened and expanded plough-share. It has been 

 suggested that the reason why these earlier fishes possessed 

 such an extraordinarily strong coat of mail is that the 

 waters of these primeval epochs were hot from contact with 

 the still heated globe, and were also impregnated with strong- 

 acids or salts ; but it does not appear that it would be any 

 advantage to be boiled in a coat of mail rather than in an 

 ordinary skin. Somewhat later in the world's history, 

 that is to say at and about the period when our coal was 

 formed, fishes with an armour of a different type were very 

 abundant ; many of the same groups also occurring in the 

 Old Red Sandstone. In these Ganoid fishes, as they are 

 scientifically termed, the body (Fig. 2) was often covered with 



Fi(i. 2. — AUanoiii Fisw (Osltiilepis) in- thk Oi.u Rkd Sandsto.n'e, 



a coat of lozenge-shaped scales, formed of bone and faced 

 with a hard coating of shming and polished enamel. These 

 scales (Ud not, as in the fishes of the present day, overlap 

 one another like the slates on a roof, but were joined 

 together at tlii'ir cdi^cs, IVci|iii.iitly with the aid of a peg 

 from one sriilc iviri\(d mto :i ^(H-ki't in the adjacent one. 

 Fishes with this turm of pkitr urmour flourished not only 

 in the Coal period but were also abundant at that later date 

 when the blue Lias clays of the cliffs of Whitljy and Lyme- 

 Eogis were laid down on the old sea-bottom. After that, 

 however, this type of armour seems to have gradually gone 

 out of fashion, and the only fish in which it now remains 

 is the Gar-pike of the American rivers, which may thus be 

 regarded as a kind of medimval knight. Tlie Sturgeons, 

 known to many of us chiefly or entirely through that 

 Kpicuiean luxury cKriare, present us witli another type of 

 armour, which is probably a survival from long past days. 

 In these gigantic fresh-water fishes the body is protected by 

 several longitudinal rows of largo diamond-shaped bony 

 ))lates, which are not connected witli one another. \\'hether, 

 however, this nuiditication of ])liite-annour is derived from 

 a complete suit, and is thus somewhat analogous to the 

 Life-(iuardsman's cuirass, or whether it was always of the 

 same type as at present, is one of those questions which 

 does not at present admit of a decisive answer. In contrast 

 to the Ganoid fishes, where we see a gradual dying out of 

 the old mail-clad types, we may notice the case of the 

 Sharks and Rays. These fishes seem to have taken a 

 moderate course in regard to armour, avoiding on the one 

 iuind tlu' plate-armour of the Ganoids, and on the other 



the light scale-armour of the fishes of to-day. In most of 

 these fishes the skin is studded with very small bony 

 granules, and thus has a rough file-like structure, being 

 commonly knowTi to us under the name of Shagreen. 

 These fishes, be it noted, while among the earliest known 

 forms, are still extremely abundant, and thus present a 

 striking instance of the advantage of a middle course in the 

 struggle for existence. 



By far the great majority of the fishes of the present day 

 lielong, however, to a group wliich seems to have made its 

 appearance shortly before our Chalk was deposited, and is 

 now the dominant one. These modern fishes have 

 sui-ci'i'dcd in entirely getting rid of the plate-armour of the 

 Ganoids, for wliich they have substituted a much lighter 

 scale-armour formed of the well known over-lappmg horny 

 scales which give the silvery lustre we admire so much in 

 the roach and salmon. The same type of armour also 

 obtains in the Barramunda of Queensland (Fig. 3), which 



Fig. 3. — The Barramunda {Ceratodus) of Queensland, showing 

 ovKRi.AiM'iNG Scale-armour. 



belongs to an older group. Whereas, however, the majority 

 of the fishes of the present day have adopted this Ught 

 scale-armour in place of the old-fashioned plate-armour, 

 a few have struck out a new line in 

 the development of a different type 

 of bony coat of mail. Thus the 

 tropical Coffer- and File-fishes have 

 ---^ a protective coat of bony plate- 



armour with a sculptiu-ed outer sur- 

 face, so locked together as to form 

 a box-like structme investing the 

 SHOWING Plate-armour, entire body. Again, among the fresh- 

 water Cat-fishes there is one genus 

 in which the body is covered by a cuirass of overlapping 

 plates formed of solid bone. Perhaps, however, the most 

 peculiar kind of armour in the entire class is found among 

 some of the well-known Globe-fishes, which are also so 

 remarkable for their habit of inflating their bodies into a 

 balloon-like shape. In these fishes, as is shown by a 

 preparation m one of the cases already alluded to ui the 

 Natural History lluseum, the body is protected by a coating 

 of long spikes, each of wliich may be as much as two inches 

 in length, and is mserted in the skm by a flat and expanded 

 plate of bone. 



As a whole, then, in spite of the exceptions last mentioned, 

 which according to the time-honoured phrase only serve 

 to prove the rule, the fishes appear to have come to the 

 same conclusion as the more advanced divisions of the 

 human race, that a massive armour for the protection of 

 the body is an encund)raiici' rather than an advantage 

 as a means of protection against attack. 



The .same story is told still more clearly in that group of 

 animals now represented by the frogs, newts, and their 

 allies, which are popularly reckoned among Reptiles, but 

 which Naturalists, with that tendency to multiply terms for 

 which they are so celebrated, distinguish as Amphibians. 

 Thus during and for some time after that distant epoch 

 to which we have already referred, when the coal 

 forests waved over what is now Britain, there lived a 

 number of newt-like Amphibians, termed, from the com- 

 plicated internal foldings found in the teeth of many of 

 them, Labyrinthodonts. In these creatures, of which the 

 petritied footmarks are often found in the sandstones of 



