346 Dr. A. S. Packard, Jun., on the 
Chilognaths, the two anterior becoming the two pairs of mali- 
pedes of the present Chilopoda. Thus the first six appendages 
of the embryo Geophilus correspond to the antennee, two pairs 
of mouth-parts and three pairs of legs of the larval Julus. 
The phenomenon of two pairs of limbs to a segment, so 
unique in 'T'racheata, may be explained by reference to the 
Phyllopoda among the Branchiata. The parallel is quite 
exact. The larve in both groups have but a single pair of 
appendages to a segment; the acquisition of a second pair 
in the Diplopods is clearly enough a secondary character, and 
perhaps necessary in locomotion ina cylindrical body with no 
sterna *. 
The larval Ju/us and the ancestral Chilognaths were hexa- 
pod Tracheata, but sufficiently different to indicate plainly 
that the Myriopods branched off from a much more primitive 
form than the Scolopendrella-like hexapod ancestor, and which 
form somewhat agrees with our hypothetical leptiform ancestor 
of all Tracheata, 
The Myriopods also differ from Hexapoda in that the genital 
armature of the male (the females have nothing corresponding 
to the ovipositor of Hexapoda) is not homologous with that of 
true insects; moreover, the armature is not homologous with 
the limbs or jointed appendages of the myriopodous body. 
On the contrary, the apparatus of hooks arises from the ster- 
num of the sixth segment, between, but a little in advance of, 
the origin of the eighth pair of legs. It should be observed 
that the legs in Myriopods are outgrowths between the tergites 
and sternites, there being no pleurites differentiated, and in 
this important point also the Myriopods are quite unlike the 
Hexapodous 'l'racheates. 
Affinity and Systematic Position of the Pauropoda.—The 
nearest living forms which approach the larval Diplopod are 
Pauropus and Eurypauropus. These organisms are practi- 
cally primitive Diplopods. Looking at the lowest Chilognath, 
Polyxenus, and comparing Pauropus with it, it will be seen 
that the latter scarcely differs from it ordinally. Pauropus 
has a head with a pair of antennee and two pairs of mouth- 
appendages. ‘The antenne are quite unlike those of any other 
* It is plain that, as Balfour suggests (‘Comparative Embryology,’ 
p- 824), the double segments have not originated from a fusion of two 
primitively distinct segments. There is, however, a misconception as to 
the nature of the “double segments.” They are not so in fact. The 
scutes are single, undivided, but the ventral region is alone imperfectly 
double, bearing two pairs of appendages, just as single segments of Apo- 
didee may bear from two to six appendages ; the differentiation is confined 
to the ventral limb-bearing region and limbs alone; the dorsal part of the 
segment does not share in the process. 
