DISTRIBUTION OF ORGANISMS. 187 



for that function on the mouth, and in the eight free filaments 

 seen in some species extending forward from around the 

 mouth, " representing," as Professor Owen remarks, "the 

 eight ordinary arms of the Cephalopoda Dibranchiata, but 

 arrested in their development by reason of the preponderating 

 size of the caudal extremity of the body, which now [that is, 

 in the fish] forms the sole organ of locomotion." The lancelot, 

 one of this family, is so extremely humble in organization, that 

 Pallas mistook it for a limax (a gasteropodous mollusk), and 

 it has only of late been finally established among the fishes. 

 Some difficulty has been experienced in seeing true affinity 

 between the baglike figure of the mollusk and the cylindrical 

 elongated form of the fish ; but it has been suggested that the 

 mollusk is, as it were, the fish doubled-in or inverted upon 

 itself : hence the end of the alimentary canal so near to the 

 mouth. The inversion reversed or undone, makes the fish. 

 These appearances of propinquity are most interesting. If 

 they do not indicate genealogical connexion, it is difficult to 

 account for them. On any other supposition, how should 

 such peculiarities of organization be seen exactly at this point 

 in the animal scale 1 The fishes here spoken of are not dis- 

 covered in a fossil state. For this their want of hard parts 

 unfitted them j but they are classed with the Chondroptergii, 

 or cartilaginous fishes, which, we have seen, are amongst the 

 first found in the ascending series of rocks. The affinity and 

 the geological succession are therefore in perfect harmony. It 

 is important to remark the progress from entirely soft animals, 

 to an order bearing cartilaginous plates to protect a rudi- 

 mental brain ; from these, again, to an order having a skull 

 and vertebral column of cartilage j a series of advances entirely 

 conformable to phenomena seen in individual development. 

 Nor is it to be overlooked that the presumed progeny exhibit, 

 in their voracious character, and the functions they serve in 

 nature, a perfect family likeness to their ancestry. The car- 

 tilaginous fishes were the chief police for keeping down the 

 redundant life of the Devonian and Carboniferous seas, as the 

 cephalopoda had been at an earlier stage of the existence of 

 the globe. 



The approach made by the annelides to some of the humbler 

 forms of fish 1 indicates another passage from the invertebrate 

 into the vertebrate animals; and this passage may have 



1 " It is rather ' the approach made by some of the humbler forms 

 of fish to the Annelides.' . . . The lancelot has many striking points of 

 conformity to the Annelides." MS. Notes of a Physiologist. 



