with Observations on the General Ai'rangement of the Articulata. 295 



throughout life, and it is by means of this that we are enabled to determine 

 with precision the identity of the different parts of the organ. Even so early 

 as \X\& fifth period of growth it becomes in part consolidated with the episternal 

 plates of its segment, in the formation of the broad under surface of the head. 

 The femur {g) continues to enlarge, and forms the chief portion of the man- 

 dible; while the tibial (h), metatarsal (i) and tarsal joints {k) are all more and 

 more arrested in development, and at length remain but simple rings, that 

 support and bend the prehensile extremity of the organ, — the enormously de- 

 veloped claw (m). An additional proof of the identity of the chief portion of 

 the mandible with the femur of the legs is afforded in its armature. The 

 internal angle of the distal extremity of this part in the Scolopendridce is 

 usually developed into a long process or spine (fig. 22, s), which is sometimes 

 furnished with one or more tubercles. I have designated this process in the 

 mandible the mandibular tooth, and have employed it in the description of 

 species. The femur of the posterior legs is also developed into a long process, 

 precisely similar to that of the mandibles. The identity of these parts is even 

 more strongly marked in Cermatia, in which the under surface of the femur of 

 all the legs is armed with a strong spine, while a similar spine exists at precisely 

 the same place on the corresponding portion of the mandibles. In Scolopendra, 

 Lithobius and Cermatia one of the tarsal articulations has disappeared, and the 

 others with the tibia are reduced to their minimum. In Mecistocephalus, 

 Cryptops and Geophilus the coxa becomes in part united with the episternal 

 plates by simple anchylosis, but remains entire in Scolopendra and Lithobius. 

 The sternal and episternal plates are largely developed and consolidated toge- 

 ther, to form the broad inferior labium, at a very early period in the young 

 Geophilus, and are enlarged to their fullest extent in Mecistocephalus. The 

 original distinction of these parts is clearly indicated in Cryptops anomolans 

 (fig. 26.), and more decidedly in some Scolopendrce. In Lithobius and Cermatia 

 the sternal plates are almost entirely atrophied, but the episternal and epimeral 

 are expanded to form the whole of the broad labium. They are perfectly 

 distinct from, but articulated with the narrow sternal portion of the segment. 

 In the very young Lithobius (fig. 30.) the episternal plates of the basilar seg- 

 ment are two curved, elongated laminae {b), perfectly distinct, and widely sepa- 

 rated from each other in their middle portion, with a broad interspace between 



