viii PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. 



Crustaceans. There is an incompleteness and want of development 

 in the form of their body, that strongly reminds us of the embryo 

 among the crabs." Agassiz : Prin. Zool. p. 193. 



" It appears that none of the orders [of Crustacea] usually classed 

 as of the highest organization occur in the Silurian strata," Pro- 

 fessor Phillips : Mem. Geol. Survey, ii. 



"Almost all the genera of Trilobites seem to be the prophetic 

 images, in a gigantic form, of the diiferent types the Crustacea pre- 

 sent in their embryonic state." Agassiz, at the Scientific Meeting 

 at Charlestoivn, 1850. 



Cephalopoda. " They .all bore a much greater resemblance to 

 the nautilus than the cuttle-fish, and in this respect seem to exhibit 

 the same peculiarity that has already been so often alluded to, namely, 

 the usual introduction of groups of species possessing the lower or- 

 ganization of their tribe in the earliest formed strata of the earth." 

 Ansted : Pic. Sk. Creation, p. 42. 



: It may perhaps be inferred as a general result, that the abun- 

 dance of cephalopodous life in these strata is inversely as their anti- 

 quity; that the series of these animals was more and more diffused 

 and augmented in number as time elapsed, till the termination of the 

 Silurian deposits." Professor Phillips : Mem. Geol. Survey, ii. 



" Among the higher mollusca, a prominent place in the earlier 

 formations was occupied by that group which presents the least de- 

 velopment of the distinctive characters of the Cephalopod class, and 

 which has much in common with the testaceous Gasteropods." 

 Carpenter : Gen. Physiology, 345. 



7. THE EARLY FISHES WERE LOW, BOTH WITH RESPECT 

 TO THEIR CLASS AS FISHES, AND THE ORDER TO 

 WHICH THEY BELONG. 



' The Sturgeon and the White-fish are two very different fishes ; 

 yet, taking into consideration their external form and bearing 

 merely, it might be questioned which of the two should take the 

 highest rank ; whereas the doubt is very easily resolved by an exa- 

 mination of their anatomical structure. The White-fish has a 

 skeleton, and moreover a vertebral column composed of firm bone. 

 The Sturgeon, on the contrary, has no bone in the vertebral column, 

 except the spines and apophyses of the vertebrae. The middle part 

 or body of the vertebra is cartilaginous; the mouth transverse and 

 under the head ; and the caudal fin is unequally forked, while in the 

 White-fish it is equally forked. 



' If, however, we observe the young White-fish just after it has 

 issued from the egg, the contrast will be less striking. At this 

 period the vertebrae are cartilaginous, like those of the sturgeon ; its 

 mouth also is transverse, and its tail undivided ; at that period the 



