782 EfipoHT— 1900. 



and rivers of the glohe were evolved from tliem there can be no reasonable doubt, 

 while it is equally clear that they branched off at an early period, as already in 

 the Trias we find the first representatives of the order of Isospondyli, which 

 contains our familiar Herrings, Salmonids, Elopids, Scopelids, &c. For Dr. Smith 

 AVoodward has not only definitely placed the Jurassic Leptolepidre and Oligo- 

 plenridce in the Isospondyli, but also the Pholidophoridse, which appear in the 

 Trias and extend to the Purbeck. And it is of special interest that in the 

 Pholidophori the scales are still brilliantly ganoid and mostly retain the peg-and- 

 sochet articulation, while in the allied Leptolepidoa, although they have become 

 thin and circular, a layer of ganoine mostl}' remains. 



With the Isospondyli we now get fairly among the bony fishes of modern 

 type — Teleostei as we used to call them — to which other sub-orders are added in 

 (iretaceoua and Tertiary times, and which in the present day have assumed an 

 overwhelming numerical preponderance over all other fishes. The prevalent form 

 of scale among these is thin, rounded, deeply imbricating, and with the posterior 

 margin either plain (cycloid) or serrated (ctenoid). But that these 'cycloid ' and 

 * ctenoid ' scales are modifications from the rhombic osseous ' ganoid ' type we 

 cannot doubt after what we have seen. It is indeed strange that the same 

 tendency to the change of rhombic into circular overlapping scales should have 

 occurred independently in more than one group. 



For reasons given at the beginning, and also because I fear I have already 

 exceeded the limit of time usually allotted to such an Address, I must now stop. 



But in conclusion I may allude to a well-known fact regarding the tail of 

 these modern fishes, the bearing of which on the doctrine of Descent is sufficiently 

 clear and has long been recognised. 



We have seen that the completely beterocercal tail of the typical Acipenseroid 

 becomes, by abortion of the upper lobe and shortening of the axis, the semi- 

 heterocercal one of the Lepidosteids, in most of which, however, the want of 

 symmetry is still perceptible externally by a short projection or ' sinus ' of scales 

 Avhich is directed obliquely upward at the beginning of the top of the fin. In the 

 ordinary bony fishes and in some Lepidosteids also the caudal fin becomes like- 

 wise svmmetrical, as seen from the outside ; generally also bilobate, though the 

 upper lobe is not that of a Palreoniscid or Sturgeon. This condition of tail has 

 been long known as ' homocercal.' But in many such homocercal tails, when we 

 dissect away the skin and soft parts, the upward bend of the vertebral axis is 

 revealed, and in some, as in the Salmon, the extremity of the vertebral axis is 

 continued as a cartilaginous style among the rays near the upper margin of the fin. 

 But there are many others, such, for instance, as the peculiarly specialised group of 

 Pleuronectidffi or flat fishes, in which the skeleton of the caudal extremity looks 

 quite symmetrical, but yet in the embryo the extremity of the notochord is seen 

 to have an upward bend, showing that the homocercal tail is indeed a specialisa- 

 tion on the old beterocercal one. It is strange that though this embryological 

 fact was long ago pointed out by Agassiz, and though he noted its great interest in 

 connection with the prevalence of heterocercy among the Pahcozoic fishes, yet he 

 remained to the end an opponent of evolution. But this is just one of these 

 instances in which Phylogeny and Ontogeny mutually illustrate each other. 

 Why, otherwise, should the tail of the embryo stickleback or flounder be betero- 

 cercal ? 



Incompletely as I have treated the subject, it cannot but be acknowledged 

 that the palajontology of fishes is not less emphatic in the support of Descent 

 than that of any other division of the animal kingdom. But in former days the 

 evidence of fossil ichthyology was by some read otherwise. 



It is now a little over forty years since Hugh Miller died : he who was one 

 of the first collectors of the fossil fishes of the Scottish Old Red Sandstone, and 

 who knew these in some respects better than any man of his time, not excepting 

 Agassiz himself. Yet his life was spent in a fierce denunciation of the doctrine 

 of evolution, then only in its Lamarckian form, as Darwin had not yet electrified 

 the world with his ' Origin of Species.' Many a time I wonder greatly what 

 Hugh Miller would have thought had he lived a few years longer, so as to have 



