86 



On the Classification of Animals 



When, however, the posterior extremity is, in magnitude and im- 

 portance, a part of the main body structure itself, as in Snakes 

 and Fishes, the case is properly an example of multiplicative 

 degradation. 



The abnormal number of segments under the multiplicative 

 method may arise from a self-subdivision of enlarging normal 

 segments, or from additions beyond the range of the normal 

 number. The many joints of the antennse in Crustaceans of the 

 Cyclops group, the writer has shown to result through the former 

 method, and the multiple segments of Phyllopods m,ay be of the 

 same origin : but there are no facts yet ascertained that would 

 refer the multiplication of segments in Myriapods and Worms to 

 this method. 



Viewed on the ascending grade, this method is the limitative. 

 D. Structural. 



7. Analytic. — Exhibited in a resolving of the body-structure, 

 or of an organ, more or less completely, into its equal normal 

 elements, or in a tendency to such a resolution. 



A relaxed state of the cephalic power leads to a relaxed and 

 elementally-constituted structure. When this method charac- 

 terizes strongly the general structure, the form is usually degra- 

 dational ; as in Myriapods, Worms, larves of Insects, — these 

 structures consisting of a series of nearly similar rings (the 

 normal elements of an Articulate), without a subdivision into 

 head, thorax, and abdomen. Fishes, of the Vertebrate type, are, 

 as nearly as may be, in this elementalized condition. An ap- 

 proximation towards analysis or resolution of the body appears 

 in the absence of the constriction between the head and thorax in 

 Spiders and Crustaceans ; and still further, in the absence of the 

 constriction between the thorax and abdomen in the lowest of 

 Spiders, — the Acaroids. - 



Under this method, there is, in no case, among adults, or larves, 

 a complete analysis or resolution of the head into normal seg- 

 ments ; the closest approximation to it, Insecteans and Crus- 

 taceans, occurs in the Gastrurans (Squilla group). But here the 

 mandibular, and one, two, or more maxillary segments are still 

 united. In an Insect, the head contains six normal segments, and 

 the thorax three ; and yet the thorax has 3 to 5 times the bulk 

 of the head ; — showing a condensation in the head-part equal to 

 6 to 10 times that of the thorax. Concentration in an animal 

 structure is therefore eminently cephalic concentration, or, in a 

 word, cephalization, — the head being the part most condensed, and 

 least liable to occur resolved into its elements. 



The analytic method, viewed on the ascending grade, is the 

 synthetic. 



