1903.] PACKARD—CLASSIFICATION OF ARTHROPODA. 157 
Chilopoda. In Polydesmus the method of formation of the blas- 
toderm more resembles that of the Crustaceans and Arachnida than 
that of Chilopods. 
The larva of the Diplopods, though bearing but three pairs of 
legs, differs from that of any insect in that these limbs are not 
appended to consecutive segments ; either the second or the third 
segment in different species of Julus being legless, while in Blaniulus 
the legs are borne on segments 2 to 4 behind the head.1 The new 
double segments with their two pairs of legs arise at successive 
molts, so that the animal undergoes a partial metamorphosis ; while 
the Chilopods are hatched in the form of the adult, being poly- 
podous. 
Pauropopa. Nothing has been added to our knowledge of these 
forms since the publication of the thorough works on them by 
Kenyon and by Schmidt. 
The group was regarded as an order (Pauropoda) by Lubbock. 
Kenyon, however, created the order Protodiplopoda, including in 
it Pauropus and Polyxenus. 
The Pauropoda are regarded by Kenyon as degenerate Diplo- 
pods, owing to the absence of tracheal and circulatory systems, 
and distantly related to Polyxenus; on the other hand, the sim- 
plicity of the segmentation, the fact that there is but a single pair 
of legs to a segment, and other features pointed out by Kenyon, 
lead us to provisionally regard the group as a class more primitive 
and distinct from the Diplopoda. The number of mouth-appen- 
dages is the same as in the Diplopods; the genital aperture opens 
on the third trunk-segment, and the testis is situated above the 
intestine (the ovary below). 
History of the Opinions regarding the Taxonomy of the Meropoda. 
—The first writer to doubt the naturalness of the group Myriopoda, 
and to state that the Chilopoda and Hexapoda were more nearly 
allied than the Chilopoda and Diplopoda, was Pocock,? in 1887. 
A year later Dr. Kingsley ® arrived independently at the same opin- 
ion, adding the anatomical data in support of this view. 
1 The young of Polyzonium, however, is hatched with four pairs of legs, borne 
on each of the first four trunk-segments (Rimsky-Korsakow, Travaux Soc. Imp. 
Naturalistes de St. Petersbourg, xxv, 1895, Pl. 1, Fig. 8). 
2 Annals and Mag. Nat. Hist., xx, October, 1887. 
3 American Naturalist, December, 1888, p. 1118. 
