Chap. II. DIFFERENT MODES OF LIFE. 365 



thougli not nearly- so mncli so as in Testudo. After the nerves have passed the 

 skull-box, they run, in Trionyx, first sideways in a right angle, and after a short 

 while, in a second knee, forward to the eyes. In Testudo they run also side- 

 ways in nearly a right angle, but ])ass into the eyes without fonning a second 

 knee ; in Emydoidai they bend in a wide angle, or rather in a curve, fonvard 

 and sideways; while in Chelydra and Cinosternmn they run very much as in Tri- 

 onyx ; finally, in Chelonii proper they run forward and sideways, as in Emydoid39. 

 Though there can be no doubt that the brain is the organ to which all the 

 passive and the active manifestations of the psychical life of vertebrate animals 

 must be referred, nothing is yet known of the ways in which the peculiar kinds 

 of psychical manifestations of an animal are connected w'ith the peculiarities of 

 structure of its brain. This is a field hardly touched yet by naturalists, though 

 a knowledge of these relations alone can give its deeper value to the morphol- 

 ogy of the brain. Comparative anatomists must confess, that thus far the innu- 

 merable modifications in the form of the brain of Vertebrata have in no way 

 been brought into causal relation with the peculiar psj-chical faculties of the 

 animals in which they are observed. Nay, animals which have entirely diflerent 

 habits have sometimes identical brains, for instance, Salmo and Coregonus; while 

 others, which liaixUy difler in their mode of life, present great diflerences in this 

 respect, for instance, Acipenser, and the large species of the Catostomus tribe. 



SECTION XI. 



DrFFERENCES IN THE MODE OF LIFE OF TESTtTDINATA. 



A knowledge of the mode of life of auinuds is generally considered as fur- 

 nishing, at the outset, a test of their internal organization, and the means of 

 ascertaining the degree of their affinity. Although this is true in a certain 

 sense, the limits within wliich there exists such a correlation between the habits 

 of animals and their structure arc not at all defined. Among Mammalia, it 

 would seem as if the mode of life coincided with the limits of the orders, if 

 we take, as genuine orders, the leading divisions adopted in that class ; though 

 wo find already here frugivorous and insectivorous Chiroptera, etc. Among Birds, 

 the tliet is still less restricted to the orders; we find herbivorous and ])iseivorous 

 species in the same family, for instance, among the Ducks. Among Turtles, we 

 have seen that the limits, within which the habits, the mode of life, and the 

 diet, are the same, coincide with the natural lunits of lamihes. The Chelonioida) 



