30 ILLINOIS BIOLOGICAL MONOGRAPHS [30 



MUSCULATURE 



The muscle systems of the parthenitae and the cercariae are confined, 

 for the most part, to the peripheral and splanchnic regions. The peripheral 

 muscles consist of an outer series of radial muscle fibers and an inner series 

 of longitudinal fibers. A third series, the dorsoventral, which is common 

 in the adult forms, is suggested at times in the body of the cercaria. The 

 muscles of the intestinal tract consist of a longitudinal and a circular series. 



The peripheral system Hes directly beneath the basement membrane. It 

 opens interstitially to permit the growth of the processes of the parenchyma 

 cells which secrete the basement membrane. The outermost layer is the cir- 

 cular series. It may consist of a single band one cell in thickness or it may in- 

 clude a cyUndrical band several layers thick (Figs. 37, 54, 97, 128). Within this 

 is the longitudinal series. Usually here the individual fibers of the bundles 

 are separated from one another by a considerable interval. The fibers are 

 longer and fewer than those of the circular series. A section of an adult trema- 

 tode shows, in addition to these, an oblique series of fibers. These oblique fibers 

 give the appearance in section of a diamond pattern. In another type, the 

 dorsoventral, the fibers run at right angles to the frontal plane. In the holo- 

 stome cercaria (Fig. 54) no such series is found, altho the longitudinal series 

 is so arranged that the fibers are on edge and might be taken for the dorso- 

 ventral series. The view of Bettendorf (1897:315, 316) that the "Epithelzellen" 

 of Blochmann are really longitudinal muscles, can not be considered valid, 

 since in the same sections the former are indifferent to stains and the latter 

 are deeply stained by the same methods of technic. 



In the oral and acetabular suckers and frequently in the pharynx there 

 exist the transverse, longitudinal and oblique series of muscle fibers, inter- 

 woven into an inseparable complex. These are best developed in the Am- 

 phistomata. Since the redia which produces germ balls is an adult and the cer- 

 caria is an immature individual, it is not surprising that the pharynx of the 

 redia is fibrous, with few nuclei and large vacuoles, while the pharynx and 

 suckers of the cercaria are composed of cells practically undifferentiated. In 

 the rediae the fibers can be traced to the myoblasts. 



The main deep-seated system of muscles for the cercaria consists of the 

 muscle band series of the digestive tract. In the holostome (Fig. 54) an 

 additional muscular activity has been assumed by the cirrus pouch. Aside 

 from these no muscle striae are developed in connection with the genitaUa in 

 the larva. The ceca of the digestive tract are covered with an outer and an 

 inner series. The former are longitudinal fibers and the latter are circular 

 fibers. This is in conformity with the muscular layer studies made on 

 other Platyhelminthes. 



Histology of the muscle cells. When Bettendorf (1897) showed the 

 connection between the muscle fibers and the myoblasts an important step 

 was made in the knowledge of the intimate structure of the trematode muscle 

 cell. The present study corroborates Bettendorf 's work. . The nuclei of 



