188 AFFINITIES AND GEOGKAPHICAL 



taken place in the Upper Silurian or Devonian era, for anne- 

 lides are ascertained to have previously existed. Perhaps 

 some of the less destructive of the early cartilagines the 

 Lepidoids were such an inoffensive family have had such 



an origin. 



It might be suggested, as an inquiry worthy of the attention 

 of zoologists, whether the echinodermal line has not given rise 

 to the more recently developed fish families those which enter 

 upon the field in the cretaceous era. If the fistularidae make, 

 as appears, so near an approximation to the lowest bearers of 

 the vertebrate type, it is not easy to see how any preconceived 

 ideas regarding the order of sub-kingdoms to be passed through 

 should stand in the way, especially after so many traces of 

 similar (apparent) irregularity. The geological history of the 

 animals in question is favourable to the conjecture, for the 

 echinoderms are amongst the most conspicuous and important 

 forms antecedent to the chalk era. Looking, indeed, at the 

 enormous abundance of crinoidea in the carboniferous rocks, 

 one can hardly avoid the idea, that this peculiar form was 

 destined for some important ultimate history. It might be 

 suggested that the orders by which the fish class is thus entered, 

 are those placed by Cuvier at the bottom of the osseous fishes, 

 the Lophobranchii and Plectognathi, which indicate their near- 

 ness to the invertebrate type by many features attaching to 

 some or all of them, as imperfection and slow hardening of 

 the skeleton, deficiency of ribs and fins, low and embryotic 

 forms of mouth, dentition, and gills ; the Lophobranchii, 

 moreover, hatching their young in a pouch below the tail, 

 after the manner of a family of animals equally low among 

 the mammalia. 



In the present state of this inquiry, it is impossible to give 

 an entire genealogical tree of Being. Much must remain ob- 

 scure and unindicated. Even of what is set forth, some parts 

 must be held liable to correction under better light. Enough, 

 however, is done for the present object, if such fragments of 

 the great composite chain be shown, as afford proof that there 

 is such a thing in nature, and that the idea of genetic succes- 

 sion of advancing forms is in harmony with it. The fishes 

 form one of the obscurer portions of the animal kingdom. The 

 classifications of Cuvier and Agassiz are neither of them ad- 

 mitted to be natural ; it is therefore not to be expected that 

 any general student should be able to display the class in all 

 its genetic relations, however confident he may be, from what he 

 sees elsewhere, that such relations exist. We find, however, 



