298 CTEN0riI0R2E. Part II. 



forms of the -wholo order, such as Ocj^roe and Calyrama, are exclusively tropical, 

 Ocyroe being peculiar to the equatorial zone of the Atlantic, while Calymuia is 

 found in the Pacific as well as in the Atlantic. 



For want of materials, it would be premature, at this time, to attempt tracing 

 with 2)reeisi()n the natural boundaries of the Acalephian fauna\ But, in connection 

 with data oljtained from other classes, much may already be done towards a better 

 understanding of what zoological provinces truly are. In studying the geographical 

 distribution of animals and plants, natiu'alists have followed different methods, leading 

 to diflerent results, and bearing in different ways upon the question before us. 

 While investigating the relations under which animals and plants are placed, in 

 different parts of tlie world, in reference to the physical influences to which they 

 are exposed, we no doubt ascertain much that is of great importance for the limi- 

 tation of the fauna? ; but such studies do not lead, after all, to the knowledge of 

 natural zoological provinces, Init only to a fidler insight into the mutual dependence 

 of the organized beings, and the limiting or fostering conditions under which they 

 may live. This study, as I understand it, may end in giving us a more extensive 

 physical history of the organic world, Ijut cannot, by itself, furnish even the foundation 

 for an organic geography, that is to say, for a knowledge of the natural mode 

 of association of animals and plants of the same family or of the same class, which, 

 properly speaking, constitutes natural fauna? or zoological j^rovinces. Nay, this natu- 

 ral mode of association of a variety of animals, belonging either to one and the same 

 class or to different classes and different kingdoms, might ])e obtained without a 

 deeper knowledge of the physical influences which limit the geographical range of 

 the species considered singly. 



Again, much confusion seems to prevail among zoologists and paleontologists in 

 the use which the}' make of the Avord fauna. 8ome designate liy it a definite area, 

 within which a variety of animals appears to Ije naturally associated ; aiid I l>elieve 

 it is in this sense that the term should hereafter be exclusively used. It is 

 self-evident, that if the term fauna is applied to such circumscribed areas, and is 

 at the same time used to designate entire zones, over which many distinct zoo- 

 logical provinces may be distributed, as is frequently done when zoologists speak 

 of the ti'opical fauna, the temperate fauna, etc., two veiy different ideas are thus 

 confounded, and no accurate views can be introduced in our science, since in the 

 first case a geographical area is intended, characterized by a peculiar association of 

 various animals, and in the second case a special condjination of physical features 

 limiting the range of organized beings. It is far better here to use the exj^ressioii 

 of zone, consecrated in physical geography, and to speak of the troj^ical zone, the 

 northern and the southern temperate zones, etc. ; or, if the two ideas are to be 

 coudjined, to speak of the fiuna? of the tropical zone, in contradistinction to the 



