556 OLDEST KNOWN FOSSIL FISH. [Ch. XXVII. 



Huxley as allied to the Sturgeon, and therefore by no means of 

 low grade in the piscine class. Hence its detection in the rocks 

 lower in the series than those to which the earliest known verte- 

 brata had previously been traced, is a fact of no slight interest; 

 for they who have full faith in the doctrine of progressive develop- 

 ment will naturally expect to meet with the earliest vestiges of 

 the piscine class in still more ancient strata. They may look, 

 for example," in the Lower Silurian, or in the Cambrian rocks, for 

 representatives of such orders as the Marsipobranchii and Pharyn- 

 gobranchii, to which the Lamprey and Amphioxus respectively ,be- 

 long. Professor Huxley remarks that some might argue that fish of 

 those orders may be absent from the older rocks for the same reason 

 that they are entirely missing in all the newer ones, whether palaeozoic 

 or neozoic, namely, because they are without bony skeletons or hard 

 scales.* But the same author reminds us that the Lampreys at least 

 might have left some definite traces of their horny teeth. Besides, 

 the advocates of progression would scarcely be satisfied with such a 

 way of accounting for the total absence of all traces of ichthyolites in 

 strata more. ancient than the Upper Silurian, for, according to them, 

 the earliest types of each class resembling the embryonic states of 

 more highly organized beings, exhibit, when they are first developed, 

 a great diversity of form and structure, as, according to their view, 

 did the batrachoid reptiles, before the true saurians came into exist- 

 ence, or the saurians before the placental mammalia had entered on 

 the stage. Each primitive type, whether vertebrate or invertebrate, 

 when first it became dominant and had the world to itself, unchecked 

 in its struggle for life by the competition of rivals of more advanced 

 structure, deviated in shape and organization in an infinite variety of 

 ways, sometimes imitating in certain of its characters beings of higher 

 grade. Under favorable conditions of this kind, we might expect some 

 members of the lamprey and Amphioxus orders to have exchanged a 

 gelatinous or semi-cartilaginous spiral cord for. an ossified one, or to 

 have acquired hard and scaly dermal coverings, or even to have been 

 armed with teeth of more than horny consistency, and this without 

 departing from the types of their respective orders. Had any such 

 fossils been found in very ancient rocks, the progressionists would 

 certainly have claimed them triumphantly as corroborating their 

 views, and they are therefore bound in fairness to draw, from the ab- 

 sence of such remains in ancient strata which teem with organic forms, 

 one of two conclusions ; namely, either that the progressive theory is 

 doubtful, or that we can place no reliance whatever on negative evi- 

 dence as establishing the non-existence of certain types at remote 

 eras. The latter is the alternative to which it appears to me we ought 

 to incline in the present state of our knowledge. 



* Memoirs of Survey Decade, vol. x. p. 40. 



