94 Mr. A. S. Packard on the Development 



true jointed appendages attached to the ninth or tenth abdo- 

 minal rings or both, which are often antenniform, and serve 

 as sensorio-genital organs in most Neuroptera and Orthoptera. 

 The abdominal rings are confined, as a rule, to the two lower 

 suborders of Insects, and are homologous with the " false legs " 

 of the larvse of Lepidoptera, the abdominal legs of Myriapoda, 

 and, we believe, with the three pairs of abdominal appendages 

 or spinnerets of the Arachnids. As in the most anterior rings 

 of the head, so in the terminal abdominal rings, there only re- 

 main minute portions of the arthromere, which are tergal pieces, 

 the other two elements of the ring being rarely present, or en- 

 tirely aborted. The two opposite poles of the body are there- 

 fore fashioned according to the same laws, and are morphologi- 

 cally simply repetitions of each other. 



In conclusion, we consider that twenty rings (arthromeres), 

 as a rule, compose the bodies of insects, of which seven are con- 

 tained in the head, three in the thorax, and ten in the abdomen, 

 and that, as thus grouped, forming three distinct regions, the 

 Insects diflfer from all other Articulates, standing as a class 

 above the Crustacea and Worms. The Arachnids and Myria- 

 pods, as Mr. Scudder* has shown, agree with the Insects in 

 possessing a distinct head separated from the thorax or "pseudo- 

 cephalothorax ;" so that the Myriapoda do not form a class by 

 themselves equivalent to the Crustacea, or Worms, or Insects, 

 but, with Leuckart, Agassiz, and Dana, we would prefer to rank 

 them as an order of the class Insects f. 



In a former communication J we proposed a classification of 

 Insects into two series of suborders (not, however, agreeing 

 with the Haustellata and Mandibulata of Clairville), of which 

 the lower begins with the Neuroptera,and, through the Orthoptera 

 and Hemiptera, culminate in the Coleoptera ; while the second 

 series ranks higher as a whole, beginning with the Diptera and 

 ending with the Hymenoptera, which thus stand at the head of 

 the Articulata. The Hymenoptera diff'er from all other insects 

 in having the basal ring of the abdomen thrown forward upon 



* Proc. Bost. Nat. Hist, Soc. vol. ix. p. 6.9, May 1862. 



t The embryology of Arachnids, as worked out by Claparede, shows 

 that the larva is strikingly worm-like, distinct rings ("protozoonites") 

 appearing before the biregional Arachnid form is assumed. The embryos 

 of two genera of mites, Demodex and Acarus, are at first hexapodous, as 

 Newport has shown that of Julus, a Myriapod, to be. The close homo- 

 logies of the Arachnids and Myriapods with the Insects (Hexapoda) con- 

 vince us that the three groups, whether we call them orders or classes, are 

 as a whole equivalent to the Crustacea or Worms, 



X "Synthetic Types of Insects" (Bost. Journ. Nat, Hist. vii. 1863); 

 " How to observe and collect Insects " (Second Annual Report of Maine 

 State Survey, 1863). 



