CHAPTER SECOND. 



THE GENUS AURELIA AND ITS SPECIES. 



SECTION I, 



GENERAL REMARKS. 



The methods now pursued, in treating subjects of Natural History, are to a great 

 extent stereotyped, according to the topics under consideration. In descriptive 

 zoology it is customary to introduce short characteristic phrases, called diagnoses, 

 pointing out prominently the most striking differences among species, and to have 

 longer and more minute descriptions follow, in which every peculiarity that may 

 have been noticed is enumerated at full length; but, in a laudable zeal for fulness 

 and accuracy, it happens but too frequently that remarks are introduced in no 

 way relating to specific characters. Some naturalists make the study of species an 

 occasion of ascertaining more fully their various degrees of affinity or relationship, 

 with a view to their systematic arrangement; while others study with greater care 

 the habits of animals, or their geographical distribution, or their uses to man. In 

 comparative anatomy the modes of treatment are not less varied. Some authors, 

 devoting themselves chiefly to a thorough investigation of the structure of animals, 

 describe their organization in the minutest manner ; but we constantly find 

 structural features which may be common to an entire family, nay even to whole 

 classes, dealt with, in such monographs, as if they were specific pecidiarities of 

 the animals under consideration. Other writers aim more especially at a study 

 of the relations which exist between structures seemingly very different from one 

 another ; and thus, wliile they may acquire a deeper insight into the laws of the 

 organization of animals and trace the remotest homologies and distinguish them 

 from analogical resemblances, frequently overlook the typical differences which con- 

 stitute natural subordinate groups in the animal kingdom. Others limit their 



