X PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. 



which have the nervous system in greatest vigour the cleverest 

 fishes, so to speak. And this is the fact. 



M. Agassiz, in his Recherches sur les Poissons Fossiles, ex- 

 presses his full conviction of a harmony between the succession of 

 ichthyic types and their relation to the geological formations to 

 which they belong. " It may, indeed," he says, " be affirmed that 

 the closest connexion exists between the principal types of this class 

 and the epoch of their successive development. We have only to 

 glance at the tables of species characteristic of the formations, which 

 I published at the end of vols. 2, 3, 4, and 5 of my work, to be con- 

 vinced that each order, and even each family, follows a particular 

 progression ; that there is, in regard to each group, a beginning and 

 an apogee in its development ; that by turns they terminate by 

 becoming extinct, if they go back to a remote antiquity, or by 

 acquiring a considerable extension in the present creation, if their 

 appearance dates only from a recent epoch." 



Some of the Cartilaginous Fishes present characters in the 

 nervous and reproductive systems which the osseous fishes do not 

 possess. A few are viviparous, and manifest an affection for their 

 offspring. On these grounds, an assumption has been built, that 

 the fishes commence with the highest forms. The occurrence of 

 cestraceons in the Upper Silurians is particularly insisted upon as 

 evidence for this conclusion. Nevertheless the general inferiority of 

 the cartilagines seems tolerably well established. It is well known 

 that no family of the animal kingdom is equally high in all points 

 of structure and endowment, and that many forms, generally humble, 

 have characteristics of a comparatively elevated kind. There are 

 features of even the human organization which would place our race 

 below some of the inferior animals, if these were to be made an ex- 

 clusive criterion. The partial superiority possessed by certain 

 cartilaginous genera seems partly to relate to their place in creation 

 as destructives : they have a well-developed nervous system to 

 enable them to conquer their prey (see Explanations, pp. 49 56). 

 That the nervous system determines the character of the reproduc- 

 tive system is an admitted law in physiology (see Owen, Philoso- 

 phical Transactions, 1834, p. 359). To find, then, some of these carti- 

 lagines exhibiting a generative system superior to other fishes, is no 

 true difficulty in our course. On the very same ground the star-fishes 

 (radiata), where the sexes are in different individuals, are superior to 

 the annelides(articulata), which present "an androgynous combination 

 of simple ovaria and testes ;" yet no one would think of describing 

 the radiata generally as superior to the articulata. Or the polypes 

 might be said to be superior to the star-fishes, because in some of 

 them " the digestive canal presents an oesophagus, a gizzard, a 

 glandular stomach, and an intestine," while the latter animals have 

 only " a radiated sac with one aperture." Yet, does any one, for 

 that reason, think of placing the polypes above the star-fishes ? 



Professor Agassiz remarks* that of the five families of palaeozoic 



* Monographic des Poissons Fossiles, &c. 



