266 



On the Classification of Aniw.als 



groups, as suggested by different entomologists. The Lepismaa 

 show their degradational character in their larval forms and in 

 other approximations to the Myriapods, and the Podurellids 

 appear to be still inferior in having the abdomen elliptic in some 

 segments. 



(2.) The Orders of Spiders suggested by the principles of cepha- 

 lization are in precise parallelism with those of the Decapod and 

 Tetradecapod Crustaceans. They are, first, Araneoids, including 

 all the Pulmonates, except the Pedipalps ; second, Scorpionoids, 

 or the Pedipalps from among the Pulmonates, and the Chelifer 

 group from among the Trachearians ; third, Acaroids, 



The Araneoids or Brachyural Spiders ; the Scorpionoids, 

 Macrural; while the Acaroids are degradational. The last show 

 their degradational character in having no division between the 

 abdomen and cephalothorax ; so that, while Insects have the 

 body in three parts, head, thorax, and abdomen, and ordinary 

 Spiders in two., cephalothorax and abdomen, the Acaroids have it 

 undivided (page 86). Thus, one of the most prominent charac- 

 teristics marking the descent from Insects to Spiders becomes the 

 characteristic of a further descent among Spiders themselves— 

 illustrating a common principle with regard to such subdivisions. 

 The propriety of making the Acaroids a distinct group appears 

 therefore to be well sustained. 



The usual subdivision of Spiders into Pulmonates and Trache- 

 arians depends on internal characters, which is not the case with 

 any other subdivisions in the table beyond. Moreover, these 

 names, though seeming to mean much, are not based on any func- 

 tional difference between the groups. Spiders have many relations 

 to Crustaceans ; and it is natural that the subdivisions in both 

 should depend on the same methods of cephalization, the amplifi- 

 cative and analytic (p. 98). 



(3.) The two orders of Myriapods are examples, one of case a, 

 the other of case 6, under multiplicative decephalization (p. 85). 



The close relations between Isopods and the higher Myriapods, 

 suggest that they are of like grade under their respective types, 

 that is, betatypic. 



(4.) a. Under Decapod Crustaceans., the subdivisions are three, 

 as already remarked upon by the author.* 



The Anomurans are only degradational Brachyurans, and do 

 not represent an independent type of structure. The Schizopods, 

 similarly, are degradational Macrurans, with which they should 

 be united. The third type is that of the Gastrurans, which are 

 peculiar among Decapods, in having the viscera extending into the 

 abdomen, one of the marked degradational features of the type. 



* See also Amer. Jour, of Science and Art, vol. xxv. [2], pp. 337, 338. 



