214 ENTOMOLOGICAL NEWS. [September, 



unity. It is for this that I believe in the unity of the Arthropoda, 

 the more so, since the appendages of the head and thorax can be 

 homologized without the loss of a single member. The Arthro- 

 poda may be readily divided into two great groups by the ex- 

 tension of Pocock's division of the Tracheata; into Opisthogo- 

 goneta, with the openings of the generative organs near the end 

 of the body; and the Progoneta. with the openings near the end 

 of the thorax. The former includes Peripatus, Chilopoda and 

 Hexapoda. The latter includes Crustacea, Trilobites, Limulus, 

 Arachnida and Diplopoda. Indeed, it is the last group (Dip- 

 lopoda) that furnishes a key to the origin of the Progoneate 

 structure. At birth they are properly Opisthogoneates, but by 

 the insertion of a series of segments between the penultimate 

 and the last segments, the generative openings are left near the 

 middle of the body. Because of this and of the primitive nature 

 of the mouth-parts the Diplopoda may properly be, considered as 

 the ancestors of all the other Progoneata. 



The phylogeny of the Opisthogoneata is in a direct line. 

 Peripatus. as stated by Prof Klngsley is the most vermiform of 

 all Arthropoda. From it has come the Chilopoda, and from the 

 latter the true Hexapoda. The progress of evolution is marked 

 by cephalization and compactness. In the Chilopoda there is 

 not, as Prof Kingsley asserts (1. c. p. 38), a stigmata to each 

 segment; this is true only of the lower groups; in the higher 

 groups as the alternate segments shorten the alternate stigmata 

 disappear. 



The primitive number of cephalic appendages is three; the 

 number presented by the most primitive Arthropod, Peripatus. 

 This is the number in the Chilopoda, and in Hexapoda, as I have 

 previously shown (Am. Nat. 1893, p. 400), the first two pairs of 

 Chilopod legs have advanced to form the compound maxillae and 

 labium. So that the head of insects bears at least five pairs of 

 appendages besides the labrum, three behind the mandibles. 



The Diplopoda have come from the same stem as the Chilo- 

 poda and possess the three cephalic appendages, and in their 

 young stages but three pairs of legs; six pairs of appendages in 

 all; and this is the number possessed by Limulas and Arachnida. 

 Leading arachnologists hold that the mandibles of Arachnids are 

 homologous with the antennae of other Arthropods (see Simon, 

 Hist. Nat. d. Araig. 1893). Particularly significant is the posi- 



