with Observations on the General Arrangement of the Articulata. 283 



scutellum refer to the dorsal portion of the first, second, third and fourth sub- 

 segments in each division of the thorax. Each of these portions of the seg- 

 ments is originally composed, as now shown in the Myriapod, of a scutum 

 and two episcuta corresponding to the sternal and epistemal plates. 



Of the Appendages of the Segments. 



The analogy that exists in the anatomy of the segments of the Myriapoda, 

 as compared with other Articulata, is found also in the structure of the ap- 

 pendages, — the organs of locomotion. Each primary segment gives origin to 

 a single pair of legs. These are its normal appendages, and seem, as it were, 

 to complete its development, and to constitute it an integral structure in each 

 animal, the multiple of which constitutes a living body. 



The primary parts of each limb (fig. 1.) are the coxa (f), the femur (g), the 

 tibia (h), the tarsus (i, k, I) and the claw (m). These exist in all the Myria- 

 poda, but are less perfectly developed than in Insects. The coxa (f) is deve- 

 loped to a greater extent in the Chilognatha than in the Chilopoda. In the 

 latter order it is a short annular joint, closely connected with the tegument, 

 and inserted immediately above the middle of the episternal plate (6) on each 

 side. It is attached in front to a narrow elongated plate, the trochantin (n) of 

 Audouin, which exists in all the Chilopoda, but which is found only in a very 

 few hexapod insects. Immediately anterior to, and connected with this struc- 

 ture, on each side, are the two epimeral plates (c c), which give attachment to 

 some of the retractor muscles of the leg. These, therefore, are the structures 

 which may be correctly regarded as the basilar portions of the limb. The 

 femur (g) is the strongest, and is usually the longest portion of the organ, 

 and is attached to the coxa at its proximal, and to the tibia at its distal 

 extremity. As my object at present is only to point out those parts in the 

 Myriapoda which correspond to others well known in Insects, I shall merely 

 state that the tibia (h) is a short, subcylindrical articulation, similar in 

 almost every respect to the femur. The tarsus {i, h, l) is composed of at 

 least three articulations besides the claw {in). Each of these is rounded, and 

 somewhat tapering towards its distal extremity. The basilar one (/) that 

 articulates with the tibia I regard as a true metatarsus, a structure that is 

 very distinctly developed in all hexapod Insects. The third, or distal articu- 



VOL. XIX. 2 p 



