Extraordmary Development of the Cutaneoiia System, 39 



with the latter that we can best compare the state of the 

 skeleton of the cranium in the fishes of the old red sand- 

 stone. 



The osseous and mailed plates which cover the head of the 

 sturgeon, and which ai-e a continuation of the mailed plates 

 of the neck and sides, evidently do not belong to the same 

 system as the frontals and parietals of ordinary fishes. 

 They are cutaneous bones, developed by replacing ordinary 

 bones, which are wholly wanting in the great part of the 

 fishes of the old red sandstone, and particularly in the family of 

 the Cephalaspides, where we find the same arrangement as in 

 sturgeons. It would be vain to seek in the cephalar plates 

 of a Coccosteus or a Pterichthys, analogues of the frontals, 

 parietals, and nasals, of our osseous fishes. We find in their 

 place only carapaces, often singularly composed, and which, 

 nevertheless, form, by their union, coverings for the cranium 

 altogether as complete as those of ordinary fishes. 



This is the place to notice the extraordinary development 

 presented by the cutaneous system of the fishes of the old 

 red sandstone. Enormous bony plates often cover not only 

 the head, but likewise a great part of the body. An entire 

 family, that of the Cephalaspides, has its essential character 

 in the cuirass of the trunk, and the scales and plates of the 

 greater part of the Celacanthes of the old red sandstone, 

 greatly exceed what we witness in fishes belonging to more 

 recent formations. Unfortunately, we have not yet terms of 

 comparison in relation to the fishes of the present creation, 

 sufficiently numerous to appreciate the value of these charac- 

 ters ; because we are entirely without data respecting the de- 

 velopment of scales in general, and particularly that of the 

 scales of the Ganoides ; we have not even information on the 

 embryology of a single cuirassed fish of our epoch ; but it 

 may be presumed from the extraordinary development of the 

 cutaneous system in our ancient fishes, that these plates and 

 cuirasses are developed at a very early period in the embryos. 



Another fact, from which we may well call the fishes of 

 the old red sandstone the embryonic age of the reign of fishes, 

 is the development of their fins. We know that in all the 

 embryos of fishes hitherto examined, the vertical fins spring 



