NOMENCLATURE. 17 



previously described, or any more than we are justified in retaining the 

 name of Pluteus paradoxus for the young, Ophiura for the adult, the name 

 of Coryne for the Hydroid, and of Sarsia for the Medusa, or of Brachiolaria 

 for the embyro Star-fish, and Asteracanthion for the adult. The synonomy 

 and history of the species must show us all this, and any student of Inver- 

 tebrates will readily call up countless instances where, if the principle of 

 geographical names is once introduced, we might have half a dozen names 

 which have a stronger claim for recognition to denote the different con- 

 ditions, the various stages of growth of Echinoderms, Polyps, Acalephae, 

 Crustacea, Annelids, Insects, Molluscaj and even Fishes where the genetic 

 connection is not readily traced ; yet no one has ever thought it feasible, 

 or even advisable, to retain these connecting links, but, on the contrary, 

 all writers have attempted, as far as in their power, to show why they reduce 

 the number of appellations. We may call the various stages of growth by 

 different names, as the Pupa Chrysalis or Imago, the Zoea, the Pluteus, the 

 Nereis, Heteronereis stage, the Amphioxus stage, — but we stop there ; they 

 are simply convenient terms to denote our finite knowledge ; and in no 

 way do we lessen their value by saying that we have no accurate definition 

 of species, or by saying that species belong to the same categories as genera, 

 differing only in degree ; and so in admitting all the most zealous evolu- 

 tionist could require, it does not lessen the fact of the finite condition of 

 the differences we now notice, and which we call species or genera or fami- 

 lies or orders, as we class them in various categories. For their transition, 

 if such a transition does exist, can only take place through an infinite series, 

 which still leaves the problem capable of a definite solution within fixed 

 limits at any special time ; and this is all that is needed for our purpose. 



We know nature only through individuals, and whatever conclusions we 

 draw are based upon the examination of a number of individuals show- 

 ing a certain range of variation within definite limits, and these limits 

 we call in some cases specific, in others generic, in others ordinal ; and as 

 long as we confine ourselves to the interpretation of nature, susceptible 

 from such finite data, we need not trouble ourselves as to the metaphysical 

 existence of species, genera, etc., or because we have no suitable defini- 

 tion of species applying to all classes of the animal kingdom, which, in the 

 present state of biological science, it is absurd to expect. We are agreed 

 for the present to call certain categories specific, others generic, others 

 ordinal, and it matters only to us that we should distinctly state the 



