xviii PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. 



their suitableness to woods and thickets, and to damp and watery 

 places. " Everything points to the fact that, in the tertiary period, 

 the land was chiefly occupied by tree-like plants ; and, further, the 

 many species of willow and poplar, as also the swamp cypress (Tax- 

 odium), point to extensive swamps and morasses. . . . Such damp 

 woodlands were probably the favourite resorts of the numerous 

 Pachydermata of that age." The Brachocera, again, live chiefly on 

 flowering and herbaceous plants. 



" The water-beetles, as also the land-beetles, commenced with the 

 more incomplete forms the vegetable feeders, and only at a later 

 period were the more highly-organized carnivorous water-beetles 

 brought into existence." 



Acephala. " The Acephala afford us a not less striking example 

 of these relations between the organic characters of a well-charac- 

 terized zoological group, and the time of the appearance of its different 

 types. In order to show this connexion more distinctly, I may be 

 permitted to premise a few general observations on this class. Mr. 

 Owen was the first to show that the Brachiopods ought not to be 

 regarded as a separate class, but that they may be conveniently 

 arranged on the same line with the Monomyaires and the Dimyaires. 

 To prove this assertion by new arguments, I have only to bring to 

 mind that these fundamental sections of the class of Acephala are 

 closely allied to each other by the connexion of their principal forms, 

 and by their respective position in the midst of the ambient elements, 

 as I have shown in my memoir, Sur les monies de Jlfollusques 

 Vivans et Fossiles, to which I refer. I shall here merely state that 

 the Brachiopods exhibit an inverse symmetry when compared with 

 that of the regular Dimyaires. In the former the right and left 

 sides are of very different conformation, and the animal is constantly 

 lying on one of its sides, and the sides have been very generally and 

 erroneously regarded as the dorsal and ventral regions. The an- 

 terior and posterior extremities, on the contrary, are shaped with 

 the most perfect symmetry ; that is to say, in other words, the front 

 and hinder part of the animal cannot be distinguished, while its sides 

 show a marked difference. In the Monomyaires in general, and 

 among the Ostracese in particular, we observe a conformation inter- 

 mediate between that of the Brachiopods arid that of the Dimyaires ; 

 the sides are still very different, but now one of the edges appears as 

 the anterior extremity of the body, and the animal, still adhering in 

 the case of oysters, has no longer, in all the genera, the absolutely 

 lateral position of the inferior types ; witness the Pectens, which 

 swim freely. Lastly, among the Dimyaires, the bilateral symmetry 

 attains to full perfection, and, at the same time, one of the extremi- 

 ties of the body is sensibly characterized as the anterior. The animal 

 then assumes a position more or less vertical, the head in advance, 

 and the relation of its organs with the surrounding media is 

 analogous to those of other symmetrical animals. 



" These connexions are fully justified by the order of the succession 



