FISHES ABUNDANT. 39 



one expanded immediately from the vertebral column, while 

 the lower one is given off at a point some distance from the 

 extremity." ( 20 ) Xow it is a remarkable fact, that this one- 

 sided tail is a peculiarity in the more perfect fishes (as the 

 salmon) at a certain stage in their embryonic history ; as is 

 also the inferior position of the mouth, peculiar to the early 

 fishes. More than this : in the earlier periods of embryonic 

 life, there is no vertebral column. This organ is represented 

 in embryos by a gelatinous cord, called the dorsal cord, 

 which in maturity disappears as the vertebrae are formed 

 upon it. M. Agassiz has satisfied himself that this was the 

 nature of the organization of the early fishes, as it is that of 

 the sturgeon of the present seas. It is not premature to re- 

 mark how broadly these facts hint at the parity of law affect- 

 ing the progress of general creation, and the progress of an 

 individual foetus of one of the more perfect animals. ( 21 ) An- 

 other feature of the placoids, bringing them down towards 

 the level of an inferior portion of the animal kingdom, is the 

 distinct marks which the dermal plates bear, in many speci- 

 mens, t)f processes for muscular attachments. This suggests 

 a peculiarity of articulate animals, and powerfully hints that 

 the cartilaginous skeleton had not been, as in higher verte- 

 brata, the grand support of the frame, and the basis of its 

 strength. 



An eminent geologist is of opinion that the species of this 

 era vary locally, as far as might be expected from what we 

 see of the distribution of animal life in the present times. 

 Nevertheless, throughout the distant parts of the earth where 

 Devonian strata are found, the general characters of animals 

 and also vegetable life are nearly the same. It is further ob- 

 served, that whatever particular family is continued with 

 little change through a succession of strata, is also amongst 

 those most widely extended over the world. It is the opinion 

 of M. Brongniart, who has distinguished himself by his in- 

 vestigation of vegetable fossils, that the fuci of these early 

 seas indicate a higher temperature than now prevails at many 

 of the places where they are found. He regards this as a 



