190 CTENOPHORiE. Part II. 



If genera and families exist at all in nature, the genera above mentioned, and 

 the families to which they have been referred, or some other divisions more or less 

 nearly approaching them, really exist; and the discrepancies between the statements 

 of LinntEus, Cuviei', and Miiller, respecting their affinities, will have nothing to do 

 with the existence of the groups to which they belong, when their natural limits 

 shall be ascertained beyond controversy. The differences now so generally pre- 

 vailing among naturalists respecting the circumscription of the groups they adopt 

 do not arise, in my opinion, from inherent difficulties in the subject, but from 

 the circumstance, that, in defining groups of any kind, zoologists are too ready to 

 snatch at the first feature which strikes their eye and seems to afford a ground 

 for distinction, without making themselves thoroughly acquainted with the whole 

 range of peculiarities of the animals they stud}', and then sifting the different 

 categories of their characteristic features to lay the foimdation for a durable edifice. 

 As soon as genera and families and the higher divisions of animals begin to be 

 studied with the view of ascertaining the nature of their difference, and no longer 

 simply as means of classifying sj^ecies, we shall hear no more of the unmeaning 

 complaints about maJcing too many genera, or about useless genera, and the non- 

 existence of genera and families and the real existence of species, and the like ; 

 but shall enter upon an era of truly scientific studies in systematic zoology. 



SECTION II. 



THE NATURAL FAMILIES OF THE CTEXOFHOR^E EURYSTOM.E. 



There is a much greater uniformity among the representatives of the Cte- 

 nophorte Eurystomie than among either the Saccatai or Lobata) ; and it is not easy 

 to ascertain whether they all Ijelong to one family or not, for the simple reason 

 that very few of them have been examined with the minuteness now required 

 in the investigation of Acalephs. There is, in fact, a single figure among the 

 many thus far publislied, and representing Beroids proper, which gives an accurate 

 idea of the structure and form of one of these Acalephs, and that is nearly twenty 

 years old ; it accompanies Milne-Edwards's highly instructive j^aper on Acalephs, in 

 the Annales des Sciences naturelles for 1841. What the other illustrations are 

 intended for may be guessed at ; but it is impossible with certainty to refer 

 them to their respective species, or to ascertain the jDeculiarity of the species by 

 a comparison of the figures, and the descriptions are generally neither better nor 

 more instructive than the plates. This state of things is the more to be lamented. 



