In the record of fossil fishes he finds some features which are particularly hard to harmonize with any theory of genetic evolution.[265] Amongst the very earliest representatives of this class, even in the upper Silurian, are found remains of sharks, in his opinion the highest order of fish, and in the Devonian and Carboniferous above, of _Ganoids_ armour clad, like the sturgeon. But nowhere below the Chalk do we find a single scale of _Cycloids_ or _Ctenoids_, which in regard alike of the scales themselves, of the nervous system and of the reproductive organs, are much below the sharks, and not above the _Ganoids_. To complicate matters still more, however, the skeleton of _Cycloids_ and _Ctenoids_ is more highly organized than that of the others, and it is thus equally impossible to describe them as progressive or as retrogressive types.[266] Over and above this absence of intermediate or link forms, the witnesses who have been cited insist on the fact that those earliest found are not simple or generalized representatives of their respective types, as the theory of genetic evolution requires them to be, but are as perfectly finished and specialized as those appearing in later ages. To their testimony on this point may be added that of Professor Huxley, who while frankly confessing that he would be glad enough to find evidence in favour of such progressive modification, was constrained by his love of scientific truth to bear witness as follows:[267] The only safe and unquestionable testimony we can procure--positive evidence--fails to demonstrate any sort of progressive modification towards a less embryonic, or less generalized type, in a great many groups of animals of long-continued geological existence. In these groups there is abundant evidence of variation--none of what is generally understood as progression; and if the known geological record is to be regarded as even any considerable fragment of the whole, it is inconceivable that any theory of a necessarily progressive development can stand, for the numerous orders and families cited afford no trace of such a process. So again he declared at a later period[268] summarizing what he had said previously: In answer to the question, What does an impartial survey of the positively ascertained truths of palæontology testify in relation to the common doctrines of progressive modification?... I reply: It negatives these doctrines; for it either shows us no evidence of such modification, or demonstrates such modification as has occurred to have been very slight; and as to the nature of that modification, it yields no evidence whatsoever that the earliest members of a long-existing group were more generalized in structure than the later ones.