331] NORTH AMERICAN ASPIDOGASTRIDAE—STUNKARD 51 



and the series of movements repeated. The worm moved rapidly across 

 the field of the microscope. 



Body Covering. — Externally the worms are covered by a non- 

 cellular cuticula, which is thickest on the dorsal side of the body and 

 thinnest on the ventral surface of the adhesive disc (Figs. 49, 53). It 

 is without hooks or spines, and on the dorsal surface reaches a thickness 

 of 5/1, while on the ventral surface of the disc it is only about 1/* in 

 thickness. The cuticula is turned in at the external openings and lines 

 the external portions of the canals of the alimentary, excretory and 

 reproductive systems. 



Musculature. — Immediately inside the cuticula is the three layered 

 dermo-muscular wall, circular longitudinal and oblique muscles occur- 

 ring in the order mentioned, the circular lying next to the cuticula 

 and in all parts of the wall being better developed than the others. The 

 musculature is delicate and in some places the longitudinal and oblique 

 muscles are very scanty. The musculature of the ventral side of the 

 forebody is continued posteriorly in a thin sheet, the so-called septum 

 or diaphragm (Fig. 53), which lies just above the limiting membrane 

 of the musculature of the disc and extends posteriad as far as the caudal 

 end of the cirrus sac. In C. insignis Osborn described this structure 

 as passing posteriad as far as the caudal end of the ovary and in other 

 genera it is more strongly developed. The parenchymous muscles of 

 the body are long, often much branched, and most abundant in locations 

 where they connect different parts of the body wall with each other or 

 with adjacent internal structures. In the anterior part are many well 

 developed muscles of this type used in the movement of that region. 

 Running longitudinally among the vitellaria, as well as dorso-ventrally 

 among the viscera there are many muscle fibers. Sphincters and dilators 

 occur at the genital pore, excretory pore, at the base of the mouth funnel, 

 and at the opening between the pharynx and the intestine. 



The disc is separated from the forebody by a limiting membrane 

 (Figs. 49, 53). This membrane runs parallel to the general course of 

 the external ventral surface of the disc, projecting ventrad at each 

 ridge. Extending between this membrane and the external wall there 

 are muscle fibers, often much branched especially at the ends. The 

 ventral projections of the limiting membrane into the ridges of the 

 disc form two sides of long triangular prisms, which extend longitudi- 

 nally and transversely above the musculature of the disc. One face 

 of each of these prisms is dorsal and the opposite angles extend ventrad 

 forming the ridges which separate the disc into fossettes. These ridges 

 are composed of fibrous connective tissue in which a few nuclei are 

 embedded. 



