Fundamental Types of Organization. 85 



We have here a double series, an increasing and a decreasing. 

 The first ranges from man to the Virginian Opossum ; the second 

 continues from the Opossum to the Cetacea. The intermediate 

 members of the first series are, first, the apes, then the makis 

 (Lemur), then the plantigrade or digitigrade carnivora, and, 

 lastly, the insectivorous genera of Erinaceus, Talpa, and Ves- 

 pertilio. In the second series, the links are filled up by the Ro- 

 dentia, of which the hare forms the passage to the Ruminantia ; 

 to which follows the Pachydermata, which pass through the 

 Phoca' into the Cetacea. Thus the relations of the spinal cord 

 to the brain in these animals, entirely coincide with their other 

 natural affinities. Some writers, it is true, have regarded their 

 affinities differently, making the bat succeed to the makis, and 

 the phoca to the plantigrades. But, in the determination of 

 these affinities, we must not be swayed by a few of the more 

 obvious external marks, but by the whole internal as well as ex- 

 ternal conformation. Upon such a basis these animals will as- 

 sume the order that we have given them above. The only ana- 

 logy of the bats with the makis is in the pectoral mammae ; and 

 the phocae are intimately unconnected with the cetacea through 

 the genus Manatus. 



By this, however, I am far from asserting the mammalia can 

 be ranged in an uninterrupted series, according to the propor- 

 tions of the brain to the cord. Even in the above list, deviations 

 are found from such an order. This is owing partly to the re- 

 lative breadths of these two organs not being exactly indicative 

 of their relative masses; and to the circumstance of the number' 

 of individuals in which the masses are determined with precision 

 being still too small to justify the formation of an exact series. 

 Only, if these defects were supplied, it might be expected that, 

 in order to preserve the scale of natural affinities, the vacuities 

 of the ascending and descending series should be filled up. It 

 cannot be doubted, for example, that, in the sloths (bradypus), 

 the brain, compared with the cord, is smaller than in the makis 

 and the uppermost of the carnivora. They are, however, im- 

 mediately connected with the makis, and must be placed in the 

 series between the lemur and ursus. If the proportional breadths 

 of the organs were as 100 to 300, the descending scries from 

 man tothe opossum would change into two others, one from man 



