16$ THE DESCENT OF MAN. 



the nest, in order that they may be quickly hatched; and 

 endless similar facts could be given.* On the whole, the 

 difference in mental power between an ant and a coccus is 

 immense; yet no one has ever dreamed of placing these 

 insects in distinct classes, much less in distinct kingdoms. 

 No doubt the difference is bridged over by other insects; 

 and this is not the case with man and the higher apes. But 

 we have every reason to believe that the breaks in the series 

 are simply the results of many forms having become 

 extinct. 



Prof. Owen, relying chiefly on the structure of the brain ? 

 has divided the mammalian series into four sub-classes. 

 One of these he devotes to man; in another he places both 

 the Marsupials and the Monotremata; so that he makes 

 man as distinct from all other mammals as are these two 

 latter groups conjoined. This view has not been accepted, 

 as far as I am aware, by any naturalist capable of forming 

 an independent judgment, and therefore need not here be 

 further considered. 



We can understand why a classification founded on any 

 single character or organ even an organ so wonderfully 

 complex and important as the brain or on the high devel- 

 opment of the mental faculties, is almost sure to prove 

 unsatisfactory. This principle has indeed been tried with 

 hymenopterous insects; but when thus classed by their 

 habits or instincts, the arrangement proved thoroughly arti- 

 ficial, f Classifications may, of course, be based on any 

 character whatever, as on size, color, or the element inhab- 

 ited; but naturalists have long felt a profound conviction 

 that there is a natural system. This system, it is now generally 

 admitted, must be, as far as possible, genealogical in arrange- 

 ment that is, the co-descendants of the same form must be 

 kept together in one group, apart from the co-descendants 

 of any other form; but if the parent-forms are related, so 

 will be their descendants, and the two groups together will 

 form a larger group. The amount of difference between 

 the several groups that is, the amount of modification 



* Some of the most interesting facts ever published on the habits 

 of ants are given by Mr. Belt, in his " Naturalist in Nicaragua," 

 1874. See also Mr. Moggridge's admirable work, "Harvesting 

 Ants," etc., 1873, also " L'Instinct chez les Insectes,"by M. George 

 Pouchet, "Revue des Deux Mondes," Feb. 1870, p. 682. 



f Westwood, " Modern Class of Insects," vol. ii. 1840, p. 87, 



