III. 

 The Fore-runners of the Backl)oned Animals. 



IT has long been an interesting problem to determine the nature of 

 the orf^anisms in which first appeared the foundations of a back- 

 bone, which gave a new impetus to the evolution of the animal 

 kingdom. Embryology and Comparative Anatomy have been studied 

 in vain, Palaeontology has afforded no certain information, and the 

 rival schools of theorists are still in the midst of a conflict, at present 

 without much sure basis in fact. Whether some form of "worm" 

 gave origin to the fore-runners of the great backboned race, or whether 

 a primaeval relative of the arachnid " king-crab " turned upside- 

 down and re-arranged limbs and head — these are questions still 

 admitting of endless discussion, no doubt fruitless in their main 

 object, but desirable from the new lines of research they continually 

 suggest. We must, indeed, find the actual ancestry of the vertebrata 

 if we aim at much further progress in the quest ; and this is only 

 possible under the most unusual and accidental circumstances, unless 

 it happens that some members of each great section of that ancestry 

 possessed a calcified (or otherwise hardened) skeleton. Much has 

 been learned during recent years of the few skeletons already dis- 

 covered in the early Pakeozoic rocks, where such fossils ought to 

 occur ; and as little of this new evidence seems to have hitherto 

 attracted the attention of those most concerned in the study of 

 animal pedigrees, it may be of service to review some of the prin- 

 cipal facts. Palaeontology cannot yet solve the main difficulties, 

 but it can, at any rate, establish some suggestive points. 



With regard to the earliest traces of undoubted Chordate animals 

 in Palaeozoic rocks, the United States Geological Survey, nearly two 

 years ago, roused considerable hopes of new e\'idence from the Lower 

 Silurian (lo) ; but it now appears (ii) that these fossils are merely 

 unsatisfactory fragments, and of no value whate\er for our present 

 purpose. Equally unsatisfactory, too, are the conical teeth from the 

 Lower Silurian of St. Petersburg, previously ascribed by Rohon 

 to fishes {5). Few will doubt that these fossils belong to Chordata, 

 but beyond that determination no advance can be made. 



In the case of the remains of Chordate animals .'"rem the Upper 

 Silurian and Lower Old Red Sandstone, however, disco\eries already 

 made are more satisfactory for consideration ; and there are four 



