6 ESSAY ON CLASSIFICATION 



as it is impossible to establish precise comparisons between the differ- 

 ent stages of growth of young animals of any higher group and the 

 permanent characters of full-grown individuals of other types, with- 

 out first ascertaining what is the value of the divisions with which 

 we may have to compare embryos. My studies in this department 

 for many years have led me to pay the most careful attention to this 

 subject and to make special investigations for its solution. 



Before I proceed any further, however, I would submit one case to 

 the consideration of my reader. Suppose that the innumerable articu- 

 lated animals, which are counted by tens of thousands, nay, perhaps 

 by hundreds of thousands, had never made their appearance upon 

 the surface of our globe, with one single exception: that, for instance, 

 our Lobster (Homarus americaniis) were the only representative of 

 that extraordinarily diversified type — how should we introduce 

 that species of animals in our systems? Simply as a genus with one 

 species, by the side of all the other classes with their orders, families, 

 etc., or as a family containing only one genus with one species, or as 

 a class with one order and one genus, or as a class with one family 

 and one genus? And should we acknowledge, by the side of Verte- 

 brata, Mollusks, and Radiata, another type of Articulata, on account 

 of the existence of that one Lobster, or would it be natural to call him 

 by a single name, simply as a species, in contradistinction to all other 

 animals? ^ It was the consideration of this supposed case which led me 

 to the investigations detailed below, which, I hope, may end in the 

 ultimate solution of this apparently inextricable question. 



Though what I have now to say about this supposed case cannot 

 be fully appreciated before reading my remarks in the following 

 chapter respecting the character of the different kinds of gToups 

 adopted in our systems, it must be obvious that our Lobster, to be 

 what we see these animals are, must have its frame constructed upon 

 that very same plan of structure which it exhibits now; and, if I 

 should succeed in shoAving that there is a difference between the con- 

 ception of a plan and the manner of its execution, upon which classes 

 are founded in contradistinction to the types to which they belong, 



^ [These are Agassiz's terms for the four great branches of the animal kingdom, desig- 

 nations adopted from Cuvier's classifications. Common examples are: Vertebrata (rep- 

 tiles, mammals); Mollusks (snails, squid); Radiata (starfishes, sea lilies); Articulata 

 (worms, insects).] 



