ORGANIZATION OF ANIMALS. 197 



them in a single line according to the relative degrees of 

 complication and of perfection introduced by nature into their 

 structure, for these perfections have reference sometimes to 

 one organ sometimes to another ; and a species which, in 

 respect of the functions of nutrition for example, might be 

 much superior to another, may yet be greatly inferior to that 

 species in the organs of locomotion. As we ascend, it is true, 

 in the animal scale, from the monad to man, we remark, no 

 doubt, a progressive complication ; and it is easy to see that 

 the mollusks are superior to the zoophytes, fishes to the mol- 

 lusks, reptiles to fishes, and birds to reptiles : above all come 

 mammals. But a closer observation shows that this gradation 

 exists only between the animals which may be considered as 

 the types of each of these groups ; and it often happens that 

 certain species of an inferior group possess a structure and 

 faculties more perfect than the lowest species of a group of 

 which the chief representatives possess an organization much 

 more complex than that of all the former. Thus there are fishes, 

 as certain lampreys^ for example, which are in many respects 

 much inferior to mollusks such as the sepia, but these in 

 some measure are exceptions ; and when we trace with a bold 

 outline the grand picture of nature, it is allowable to neglect 

 these, as we overlook or neglect to observe the lesser in- 

 equalities of the soil when we desire to perceive at once the 

 general configuration of a chain of mountains. More serious 

 obstacles arise to the linear arrangement of animals, from 

 the diversity of routes followed by nature in her ascending 

 march, and from her tendency to perfect gradually each of 

 the types she has produced. Thus insects can neither be 

 placed before nor after the mollusks without violating some 

 of the most evident zoological relations ; and if we really 

 desire to express by a figure the relationship of animals, it 

 cannot be to a scale or ladder to which the animal kingdom 

 is to be compared, but to a river, which, weak at its source, 

 increases little by little as it approaches the sea, rolling not 

 all its waters in the same bed, but dividing often into branches 

 more or less numerous, which, sometimes reuniting after a 

 longer or shorter course, sometimes remaining from that 

 time forward distinct, or which at other times are lost in the 

 sands, and disappear for ever, or surging up once more, re- 

 appear at some distance, to continue their route towards the 

 common goal. 



* [Amphioxus, the Lancelet; Myxine, the Hag-fish. C. C. B.I. 



