154 ESSAY ON CLASSIFICATION. Part I. 



wliich they are themselves founded ; while orders alone are strictly defined by the 

 natural degrees of structural complications exhibited within the hmits of the 

 classes. 



As to the question, whether orders constitute necessarily one simple series in 

 their respective classes, I would say, that this must depend upon the character 

 of the class itself, or the manner in which the plan of the type is carried out 

 within the limits of the class. If the class is homogeneous, that is, if it is not 

 primarily subdivided into sub-classes, the orders will, of course, form a single series ; 

 but if some of its organic systems are developed in a different way from the others, 

 there may be one or several parallel series, each subdivided into gradated orders. 

 This can, of course, only be determined by a much more minute study of the 

 characteristics of classes than has been made thus far, and mere guesses at such 

 an internal arrangement of the classes into series, as those proposed by Kaup or 

 Fitzinger, can only be considered as the first attempts towards an estimation of 

 the relative value of the mtermediate divisions which may exist between the classes 

 and their orders. 



Oken and the physiophilosophers generally have taken a different view of orders. 

 Their idea is, that orders represent, in their respective classes, the characteristic 

 features of the other types of the animal kingdom. As Okeu's Intestinal or Gelatin- 

 ous animals are characterized by a single system of organ>s, the intestine, they 

 contain no distinct orders, but each class has three tribes, corresponding to the 

 three classes of this t3rpe, which are Infusoria, Polypi, and Acalephs. The tribes of 

 the class of Infusoria, are Infusoria proper. Polypoid Infusoria, and Acalephoid Infu- 

 soria; the tribes of the class of Polypi, are Infusorial Polypi, Polypi proper, and 

 Acalephoid Polypi; the tribes of the class Acalephs, are Infusorial Acalephs, Polypoid 

 Acalephs, and Acalephs proper. But the classes of MoUusks which are said to be 

 characterized by two systems of organs, the intestine and the vascular system, 

 contain each two orders, one corresponding to the Intestinal animals, the other to 

 the type of MoUusks, and so Acephala are divided into the order of Gelatinous 

 Acephala and that of Molluscoid Acephala, and the Gasteropods and Cephalopods 

 in the same manner into two orders each. The Articulata are considered as repre- 

 senting three systems of organs, the intestinal, the vascular, and the respiratory 

 systems; hence their classes are divided each into three orders. For instance, the 

 Worms contain an order of Gelatinous Worms, one of Molluscoid Worms, one of 

 Annulate Worms, and the same orders are adopted for Crustacea and Insects. Verte- 

 brata are said to represent five systems, the three lower ones being the intestine, the 

 vessels, and the respiratory organs, the two higher the flesh (that is, bones, muscles, 

 and nerves) and the organs of senses; hence, five orders in each class of this 

 type, as, for example. Gelatinous Fishes, Molluscoid Fishes, Entomoid Fishes, Carnal 



