September 1, 1892.] 



KNOWLEDGE. 



175 



backbone are fringes of fin-rays, so that (as shown in 

 Fig. 1) in scaled fishes the scaly part of the tail is con- 

 tinued nearly to its extremity. This type of tail is there- 

 fore exactly similar in structure to the fringe-finned type 

 of fin, and may be similarly known as the fringe-tailed 

 type. In some fringe-tailed fishes the fringes on either 

 side of the tail (as in Fig. 1) are of nearly equal depth. 

 In other instances, however, the fringe of rays on the 

 lower side is somewhat deeper than that on the upper ; 

 and a further development of this inequality results 



ever, whose movements largely partake of vigorous rushes, 

 it is probable that the forked modification of the fringe- 

 tailed type is more advantageous than would have been a 

 tail of the fan type. 



Before leaving the subject of the tails of fishes, we 

 cannot foi'bear to mention that the alteration from the 

 fringed type, with its long central axis formed by the back- 

 bone, from each joint of which springs a pair of rays, to 

 the fan-like type, with all the rays arising together from a 

 blunt and shortened backbone, is precisely paralleled among 



Fio. 4. — Skeleton of nn extinct Sliark, greatly reduced. (After Fritsch.) 



in the partially-forked tail of the sharks, where the 

 end of the backbone is bent upwards into the upper 

 and longer half of the tail, the lower lobe of which is 

 formed solely of rays. Sharks and lung-fishes have, indeed, 

 never advanced beyond one or other of these two modifica- 

 tions of the fringe-tailed type. On the other hand, the 

 compound group, including the ganoids and the bony 

 fishes, was by no means satisfied with the primitive arrange- 

 ment of matters. Starting from a fish of the fringe-tailed 

 type like the one represented in Fig. 1, we may trace a 

 gradual shortening of the central part of the tail-fin, 

 accompanied by an increasing development of the rays on 

 its lower side, until we finally reach the completely -forked 

 tail of the perch (Fig. 2), in which, as we have seen, the 

 backbone stops short of the fin-rays, and ends in an ex- 

 panded extremity from which these rays are given off in a 

 fan-like manner. The bony fishes have, therefore, not 

 only succeeded in developing the fringed fins of their 

 ancestral ganoids into those of a fan-like type, but have 

 likewise effected a precisely similar modification in the 



Fio. 5. — Eight upper tooth of an extinct lunji-fish 

 (CeratodusJ. c. Point of contact with opposite 

 tooth. (After Teller.) 



structure of their tails. That the fan-like tail of the 

 perch is an improvement as a steering organ upon the 

 fringed tail of the early ganoids there can be no doubt ; 

 and it is such an organ which alone could regulate the 

 movements of the bony fislies in the delicate manner 

 observable in a bowl of gold-fish. To the sharks, how- 



birds. Thus the ancient birds of the Jurassic rocks, 

 known under the name of Anlueopterijx, had their back- 

 bone prolonged into a long tail, from each joint of which 

 there arose a pair of feathers. Such a tail was therefore 

 essentially a fringed one. In modern birds, however, as 

 we all know, the backbone extends but a short distance 

 behind the haunch-bone, and tlien extends into a plough- 

 share-like bone, from which the feathers of the tail expand 

 in a fan-like manner, very similar to the rays of the tail of 

 a bony fish ; with the exception that, whereas in fishes the 

 fan is placed vertically, in birds it is expanded horizontally. 

 In many groups of animals besides these we have men- 

 tioned it appears, indeed, that long tails have gone out of 

 fashion, as being useless encumbrances. We have instances 

 of this in the higher apes and bats, in bears, in guinea- 

 pigs, and in the more specialized kinds of flying-dragons, 

 or pterodactyles, described in an earlier number of this 

 magazine. 



Having said this much as to the fins of the ancient 

 fishes, we may conclude our article by giving some 

 particulars relating to the geological history of the 

 baramunda, which, from the structure of its fins, we have 

 already seen reason to regard as one of the most ancient 

 types of existing fishes. For a number of years there have 

 been known from the triassic, or lowest secondary strata 

 of Europe, fish-teeth of the peculiar type of the one 

 represented in Fig. 6. The remarkable horn-like form of 

 the ridges on these teeth suggested the name of Ceratodm 

 for the otherwise unknown fish to which they pertained. 

 Nothing more was discovered as to the nature of this 

 problematical fish, and it was even doubtful in what 

 position these teeth were placed in the mouth, or how 

 many of them there were in each jaw. Thus matters 

 stood till some twenty years ago, when naturalists were 

 startled by hearing that a large fish had been discovered 

 living in the rivers of Queensland, which had teeth like 

 these problematical fossils. This fish was no other than 

 the baramunda, which, as we have seen, is one of the few 

 living species still retaining the ancient fringed fins. It 

 was found that the baramunda had one tooth on either 

 side of each jaw, placed in the same position as the figured 

 example ; and it was naturally considered that the living 

 fish belonged to the same genus as the Ceratodiis of the 

 trias. Here, then, we are confronted by the remarkable 

 circumstance that a kind of fish first made known to 



