hased on the Principle of Ceplialization. 



97 



ments are internally^ as well as externally, radiate (Phytozoic, 

 case 6). 



As Radiates have no limbs, and but imperfect senses, the higher 

 grades among them are manifested most prominently in the con- 

 ditions of the nutritive system. Some of them (the Echinoderms) 

 are superior, as animals, to the lower hemi'phytoid species, such as 

 the Bryozoans. 



2. Further exemplifications of the preceding methods of Cephal- 

 ization. — In order to give greater clearness to the explanations 

 which have been made on the preceding pages, the application of 

 the terms expressing the methods of cephalization to grades of 

 species may here be further illustrated. 



In the class of Crustaceans, the distinction between the 1st and 

 2d orders, or Decapods and Tetradecapods, depends on case a 

 under the retroferent method — a transfer of members from the 

 cephalic to the locomotive series. In connection with it, there is 

 also an exhibition, to some extent, of the analytic method, more 

 of the segments of the body in the latter being free, and all, more 

 regular or normal in form. 



Under Decapods, the difference between the 1st and 2d tribes, 

 the Brachyural and Macrural, depends mainly on the amplificative 

 method — there being in the latter, by an abrupt transition, greater 

 length and laxness before and behind. Under the analytic^ also, 

 the lengthened abdomen in the Macruran has its normal number 

 of segments and members. 



Among the subdivisions of Macrurans, the retroferent method 

 appears prominently in the transfer of force from the frst pair of 

 legs to the second^ and, among the lower genera, to the third pair 

 (see p. 83) ; the ampUficative, in the length of antennae in some 

 families, and in the length of abdomen as compared with that 

 of the cephalothorax in others ; the elliptic, in the absence of pos- 

 terior cephalothoracic members, and also the obsolescence of the 

 abdominal members in many Scliizopods or degradational Macru- 

 rans ; the pervertive, in the outer maxillipeds taking the form and 

 functions of feet, as in many inferior Macrurans. 



Under Tetradecapods, the difference between the 1st and 2d 

 tribes, or Isopods and Amphipods, depends on the very same 

 methods as that between the 1st and 2d under the Decapods ; that 

 is, on the ampUficative, as shown in the greater length of cephalo- 

 thorax and the elongated abdomen, and on the analytic^ the 

 lengthened abdomen having its normal segments and approximately 

 normal members. 



Under the Amphipods, the ampUficative method is variously 

 illustrated ; the elliptic in the obsolescent abdomen of the Caprel- 

 lids, as well as in the absence or obsolescence in many species of 

 two pairs of thoracic legs. 



NEW SERIES. VOL. XIX. NO. I. JANUARY 1864. N 



