Chap. I. PSYCHOLOGICAL DEVELOPMENT. 297 



direct relation to the development of the organs of the senses and of the brain ; 

 while the motions are dependent upon the development of the muscular system. 



Now, accurately to determine tlie standing of the Turtles in their class, as 

 far as their psychological development is concerned, a glance at the position of 

 the whole class, in its branch, may furnish some valuable hints. Though the 

 orders have been represented^ as the natural groups Avhich, being founded upon 

 the complication of the structure of animals, above all determine their relative 

 rank, it is equally true, that the classes, when compared with one another, stand 

 lower or higher, in proportion as the systems of organs which are developed in 

 them have a higher importance, or are built upon a more perfected pattern. In 

 the branch of Vertelirata, there can be no doubt that the class of Fishes, as a 

 whole, occupy the lowest position, that Amphibians rank next to them, that 

 Reptiles come next, that Birds stand above these, and that Mammalia are the 

 highest. Their whole structure shows this plainly. But, to consider only the 

 points which have a bearing upon tlie (question under consideration, it is obvious, 

 that the Fishes, in which the whole bulk of the body is one undivided mass, 

 the vertebral colunni continuous in one horizontal line with the base of the skull, 

 the muscular system uniformly extended over the whole trunk, so as to allo^v only 

 lateral motions, and the limbs reduced to branchino; dii>;itations without concen- 

 trated activity; in which the brain is only a slight enlargement of the spinal 

 marrow, and some of the organs of senses are either wanting or very imperfect, 

 while the othei-s are rather blunt and obtuse ; — it is obvious, I saj-, that this 

 class occupies, not only structurally', but also with reference to its psychological 

 endowment, a much lower position than the classes of Amphibians and of true 

 Reptiles, in which the different regions of the Iwdy are more distinct, the motions 

 more localized, the organs of the senses more perfect, and the brain larger. 



In these two classes, the preponderance of the head is already fully indicated 

 by its position, being somewhat raised above the bulk of the body and forming 

 with it a more or less marked angle, whilst in most of them the limbs are 

 detached as locomotive appendages, distinct from the trunk, though not yet so 

 free as to move with perfect independence. In Birds and Manmialia, the progress 

 is still more distinct. The dilTerent regions of the body are not only better 

 marked, they are also more diversified in their structure ; the body is no longer 

 so prone upon the medium in which the animal lives; the head has acquired a 

 special movability in connection with the highly organized organs of the senses, the 

 larger brain and the commanding position it has a.ssumed ; the motions also are 

 more diversified, not oidy in themselves, l)ut tlie anterior and posterior pair of 



1 See Part I., Chap. 2, Sect. 3, p. 150. 

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