NO. 3 INSECT HEAI3 SNODGRASS II5 



The walls of the short proventriculus are produced into six flat, 

 triangular elevations having their bases contingent anteriorly, and their 

 apices directed backward, where they all end on the rim of the wide, 

 round orifice into the ventriculus. The proventricular ridges are not 

 mere folds of the intima, for each is formed by a thick mass of the 

 underlying epithelial cells. The surface of the intima in the pro- 

 ventriculus is smooth, except for a few very small teeth on the edges 

 of the triangular ridges, and areas of minute granulations on the distal 

 halves of the latter. The posterior margin of the proventricular wall 

 is reflected outward upon itself to form a short circular fold project- 

 ing into the anterior end of the ventriculus, reaching just past the 

 openings of gastric caeca. The intima covers the outer surface of the 

 fold, but terminates at the base of this surface. The line of the latter, 

 therefore, marks the end of the stomodeal or anterior ectodermal 

 section of the alimentary canal. 



The Muscular Sheath of the Stomodeum. — The stomodeal walls 

 are everywhere covered with flat bands of muscles, which in general 

 take a transverse and a longitudinal direction, the transverse bands 

 l)eing external and the longitudinal internal; but the distribution of 

 the two sets is not such as to form a regular net-pattern on all parts 

 of the stomodeum. On the posterior two-thirds of the crop, the ex- 

 ternal transverse fibers have the form of continuous rings encircling 

 the organ, and the longitudinals run with its length. On the anterior 

 third, however, the ring muscles are interrupted laterally and dorsally. 

 and their layer is continued only on the ventral surface as a series of 

 ventral arcs ; but the fibers of a latero-ventral tract of the posterior 

 longitudinal muscles on each side curve upward on the lateral wall of 

 the crop where the circular bands are interrupted, and are continuous 

 wi'th those from the opposite side over the dorsal surface as an external 

 layer of obliquely transverse fibers reaching to the base of the pharynx. 

 On the pharyngeal tube the muscles again take the pattern of regularly 

 arranged external circular and internal longitudinal fibers. The cir- 

 cular fibers of the pharynx may belong to the interrupted set of circular 

 fibers of the crop, but the longitudinal fibers are continued irregularly 

 into the walls of the crop on the inner surface of the anterior circular 

 fibers of the latter, and they do not, therefore, belong to the same 

 layer as the posterior longitudinal crop muscles. A close study of 

 the stomodeal musculature of the grasshopper would show some com- 

 plexity of detail in the arrangement and relationship of the muscle 

 fibers, but nothing approaching the intricacy of the fiber connections 

 in the muscular layers on the pharynx and crop of the caterpillar, to 

 be described later. 



