186 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
few of the tracheae, 2V., and in Fig. 2 the muscle r. m., to which I shall 
refer later. 
In brief, the grasshopper is built up, 1, of the outer body wall; 2, of 
the inner tube, digestive canal ; and, 3, of the organs which intervene 
between the two first. Accordingly, 1 shall describe, 1st, the outer 
body wall; 2d, the intervening tissue (mesoderm); 3d, the digestive 
canal and its appendages. 226 
Before entering into the special subjects, I would remark that the 
Orthoptera, and indeed all insects, are, it seems to me, remarkably fa- 
vorable objects for histological investigations. As regards Caloptenus 
and (Edipoda, it may be mentioned in general that the cellular elements 
of their bodies are particularly large, and the nuclei of the cells distin- 
guished by being, for the most part, strikingly granulated and seldom 
exhibiting distinct nucleoli. 
ECTODERM. 
Cuticula. — It is well known that insects have an external crust or 
shell, the cuticula, which is supposed to always consist mainly of a pe- 
culiar substance, chitine, often mingled with earthy salts, such as car- 
bonate of lime and magnesia. 
In both locusts and crickets the abdominal segments present differ- 
ences in the characteristics of the cuticula of different regions. There 
are at least three distinct modifications — first, upon the dorsal arch ; 
second, on the spiracular or articular fold, which intervenes between 
the two main arches ; and, third, the main portion of the ventral arch — 
but in the locusts the dorsal and ventral portions are very similar. The 
dorsal arch, as seen in transverse sections (Fig. 3 d), is much the larger, 
coveriug the back and sides of the body, and the articular membrane, 
art., is a comparatively narrow band. Upon the living locust, or one 
recently killed, it is easy to observe that the dorsal and ventral arches 
are movable upon one another in consequence of the extreme elasticity 
and flexibility of the articular membrane (Fig. G, art). Both the dorsal 
and ventral portions of the cuticula are rigid, and, in the locusts at least, 
present a faint striation parallel to the circumference of the section. 
This striation may indicate a fibrillar structure. The inner surface of the 
cuticula presents certain peculiarities in the distribution of a reddish- 
brown pigment, probably part of the matrix, but otherwise this surface 
appears quite smooth, while the external surface is somewhat roughened, 
and is beautifully sculptured in Anabrus, as I will shortly describe. 
The thickness of the cuticula is about the same in both arches ; it has a 
yellowish tinge, shading off into brown at the posterior edges of the 
abdominal segments. The rigid portions of the cuticula are further 
characterized by the pores (Poren-canalchen) and hairs. The pores are 
quite large in diameter (see Fig. 4 p), and are widened at each end ; 
226 For tho relation of these parts the reader may also consult chapter IX of the First Annual Report 
of the Commission, pp. 257-272. 
