604 ARTHUR WILLBY. 



my theory assuming the diphyletic origin of the Tracheata 

 and the monophyletic origin of the Hexapoda.^ 



' I am aware that the assumption as to tlie monophyletic origin of the 

 Hexapoda is a very grave one to make, and I only make it in the most general 

 way. It would take one much too far afield to attempt to justify and explain 

 such an assumption in detail. At least two authors, Pocock and Kingsley, 

 have made an onslaught against the group of the Myriapoda; and Pocock 

 (R. I. Pocock, " On the Classification of Tracheate Arthropoda," ' Zool. 

 Anz.,' xvi, 1893, p. 271) has gone so far as to suggest a scheme of classifica- 

 tion, in which the group of the Myriapoda finds no place. Taking the position 

 of the generative apertures as his criterion, he divides the Tracheata (apart 

 from Arachnida) into two large groups, the Progoueata (Diplopoda and 

 Pauropoda) and Opisthogoneata (Chilopoda, Syniphyla, Hexapoda). The 

 group of the Syniphyla (Scolopendrella) is one of the utmost importance in 

 phylogenetic speculations, and there seems to have been some misunderstanding 

 about it, which however was subsequently corrected (see ' Nature,' vol. xlix, 

 p. 124). Grassi discovered in 1886 that the unpaired genital pore of 

 Scolopendrella lies on the fourth body -segment, and the same statement 

 is contained in an important memoir by Kenyon (E. C. Kenyon, " The Mor- 

 phology and Classification of the Pauropoda, with Notes on the Morphology 

 of the Diplopoda," 'Tuft's College Studies,' No. iv, 1895, see p. 136). 

 The Symphyla would seem to be related to the Chilopoda in au analogous 

 manner to that in which the Pauropoda are related to the Diplopoda. It 

 would, in fact, appear that the Symphyla are distinctly intermediate between 

 the Chilopoda and Diplopoda (Chiloguatha), having Chilopod afiinities in 

 respect of their ambulatory appendages, and Diplopod affinities in respect of 

 their manducatory appendages and generative organs (consult table at end of 

 Keuyon's memoir). Even if the two principal sub-divisions of the Myriapoda 

 were sharply divergent, I think the loss of the name Myriapoda would out- 

 weigh tbe profit of a classification which omitted all mention of the name. 

 As a matter of fact, although well-marked, the Chilopoda and Diplopoda are 

 not irretrievably divergent. 



Nevertheless, it seems not impossible that the Hexapoda have difi'ereutial 

 or heterogeneous relations to the Myriapoda. The Insecta Apterygota are 

 divisible into two well-defined sub-orders, as shown by Stummer-Traunfels, 

 namely the Apterygota entognatha (Campodeidse, Japygidse, and Col- 

 lembola) and the Apterygota ectognatha (Machilidse, Lepismidse). 

 (Rudolf Ritter v. Stummer-Traunfels, " Vergleichende Untersuchungen iiber 

 die Mundwerkzeuge der Thysanuren und Collemboleu," ' S. B. Ak. Wien,' 

 Bd. c, Abth. 1, April, 1891.) 



The Apterygota entognatha (e.g. Campodea) show strong external 

 resemblance to Scolopendrella, aud the embryonic development (Collembola) 



