516 F. G. SINCLAIR. 
nection with the nerve fibres, and on the other with delicate 
hairs which pass through the thickening of the chitin and 
project on the outside. The hypodermic thickening is richly 
supplied with fine tracheal tubes. 
The two external light-coloured patches on the front of the 
head in P. mexicanus (fig. 16) are connected with two 
small thickened marks on the brain shown in fig. 4, but my 
material was not sufficient to allow me to make out their nature. 
The ventral ganglionic cord has no striking peculiarity. 
Two pairs of nerves are given off in each segment, the 
anterior pair supplying the anterior part of the segment, and 
the posterior the posterior part. Another pair of nerves 1s 
given off from the middle of the ganglion in a rather more 
ventral position. 
GENERAL CONCLUSIONS. 
The position assigned to the Platydesmidz among the 
Myriapoda by naturalists differs very much. Lucas (7) 
placed them near the Julide on account of their mouth 
parts. Newport classed them near the Craspedosomida, 
Gervais with Polydesmide, Saussure also with the Poly- 
desmide. Humbert and Saussure in the family of Poly- 
zonide silvestri places them among the Colobognatha. 
Let us consider the characters that have led to this classifica- 
tion. ‘lhe characters of the Colobognatha according to 
Silvestri (I. Diplopodi) are these :—‘‘ Head small, eyes 
distinct or none. Mandibles and hypostoma degenerating or 
none, with the labrum forming a suctorial organ more or 
less perfect. Plural scutes free, coalesced or membranous. 
Lamina pedigera free. Foramina repugnatoria disposed in 
two lateral series beginning from the fifth somite. Segments 
30 to 108, third and two last segments apodal, first and 
second with a single pair of feet, rest with two pairs. In the 
male, external copulatory organs simple, in the seventh 
segment.” 
Now the characters of the two species of Platydesmide 
