CHAPTER II. 



AFFINITY OF THE TRILOBITES TO THE EXISTING ARTICULATA. 



SECTION XIII. 



The fact that Trilobites are now generally recognized as Articulata, saves nie the 

 necessity of speaking at greater length with regard to their affinity with the 3foIliisca ; such 

 an investigation here being the more superfluous, since I have already sufficiently shown 

 that the view is opposed by the general structure of Trilobites. For animals with eyes 

 cannot be conchiferous molluscs,* certainly not, at least when they are furnished with two 

 symmetrical compound eyes ; and this is a characteristic which also removes them from the 

 other orders of the Mollusca, and associates them beyond a doubt with the Articulata. 

 Among the four subdivisions of the Articulata, the Insects and Arachnoids (the heteronomous 

 or ArachnidcB, as well as the homonomous or Mi/riojjoda) possess, however, so constant a 

 type that it is impossible to associate the Trilobites with them ; since even the apparently 

 similar Glomerides ai'c immediately to be distinguished from the Trilobites by the constant 

 proportion of the numbers of their body rings, by the head not being shield-formed, by the 

 absence of an abdomen or tail, by the aggregate of simple eyes, by the horny, articulated, 

 numerous feet, and by many other cliaractcrs. The Trilobites, likewise, cannot be worms 

 {Vermes), the horny covering of their body, their compound eyes, and their heteronomous 

 type being opposed to such a conjecture. They are therefore Crustacea, and that not 

 only on account of those negative characters hitherto enumerated, but also on account 

 of their positive and perfectly crustacean characters. To enable the reader to understand 

 and to appreciate the latter, I shall preface this chapter by some introductory remarks on 

 the systematic arrangement of the Articulata, and particularly on the characters of the 

 Crustacea. 



SECTION XIV. 



Our present system of the animal kingdom is still tinged with one fundamental error, 

 which consists in the circumstance that we exhibit individual characters as characters of 

 groups, instead of determining the type, which is always imaginary, with scientific precision. 



* When saying this, I would guard against being supposed ignorant of tlie fact, that numerous 

 eyes have recently been observed in the species of Pecten. Previously to Krohu's interesting com- 

 munication, I had read of this structure as probably belonging to these annuals, in the ' Diet, des Scienc. 

 Natur.' torn, xxxviii, p. 236. 



