FOSSILS OF OLD RED SANDSTONE. 227 



taking the leading features of organization of structure as a 

 criterion ; but, when details of organization are regarded, 

 stretching further both downward and upward than the 

 other series ; so that, looking at one extremity, we are as 

 much entitled to call them the lowest, as the reviewer, 

 looking at another extremity, is to call them the highest 

 of their class. Of the general inferiority there can be no 

 room for doubt. Their cartilaginous structure is, in the 

 first place, analogous to the embryotic state of vertebrated 

 animals in general.* The maxillary and intermaxillary 

 bones are in them rudimental. Their tales are finned on 

 the under side only, an admitted feature of the salmon in 

 an embryotic stage ; and the mouth is placed on the under 

 side of the head, also a mean and embryotic feature 

 of structure. These characters are essential and im- 

 portant, whatever the Edinburgh reviewer may say to 

 the contrary ; they are the characters, which, above all, 

 I am chiefly concerned in looking to, for they are fea- 

 tures of embryotic progress, and embryotic progress is 

 the grand key to the theory of development. I there- 

 fore throw back to my reviewer the charge that I have 

 " clung to feeble analogies," and " kept out of view the 

 broad and speaking facts of nature." 



With regard to the alleged falsity of the crustacean 

 character of some of these fishes, and the discredit of re- 

 peating the blunders and guesses made by the first ob- 

 servers, before any good evidence was before them, I can 

 only say that, at the time when my book was written, 

 geologists and inquirers into fossil ichthyology of the 

 highest character were writing, publicly and privately, 

 of the cephalaspis and coccosteus as apparently links 

 between the Crustacea and fish, the vertical mouth of the 

 latter animal being particularly cited as a feature indi- 

 cating the intermediate character. In what the reviewer 

 calls 44 the excellent work of our meritorious self-taught 

 countryman," Mr. Hugh Miller, published in 1841, the 

 apparently crustacean character of these fishes is re- 

 peatedly referred to.f Not having access at the time to 



* Cartilage, " in many animals, forms the entire structure, and 

 in the early state of the human embryo it does the same."- -Car 

 penter's General Physiology, p. 37. 



f Mr. Miller calls upon his readers to "mark the form of the 

 cephalaspis, or buckler-head, a fish of the formation over that in 

 which the remains of the trilobite most abound. He will find,' 

 he says, " the fish and crustacean are wonderful' y alike : the fish 



