40 ILLINOIS BIOLOGICAL MONOGRAPHS [10 



Y-shaped bladder and cornua. There are only eight paired capillaries, 

 and only sixteen flame cells. This condition constitutes a reduction of flame 

 cells from the average types, a reduction which can not be entirely accounted 

 for by the small size of the species. 



2. The Echinostome type. This family of distomes is characterized by 

 simplicity of detail in the excretory system except at the head of the main 

 lateral vessel. The bladder is not markedly muscular. The pair of lateral 

 vessels arise from the anterior median region of the bladder, and not from the 

 horns of this vesicle as in the xiphidiocercariae. The main trunks do not 

 divide but proceed to the cephalic extremity along the lateral margins. They 

 sometimes receive small tributaries along their course. In the cephalic region 

 the vessel commonly flexes back on itself. Such flexure may continue back to 

 the posterior extremity of the body, as in C. reflexae (Cort, 1915, Fig. 43), or 

 may continue caudad only a short distance, reflexing a second time (C. biflexa, 

 Fig. 135). An intermediate form, C. echinata, has been described by Looss 

 (1894:191), where the first flexure continues caudad while another part is 

 reflexed cephalad. 



A modification of the type represented by C. biflexa, where the double 

 flexure is entirely within the cephalic region, is seen in C. trisolenata (Fig. 109). 

 Either the end of the flexure has been fused to the most anterior part of the 

 main vessel, or the middle portion of the system has been modified. As a 

 result a triangular channel system has been formed at the anterior end of this 

 excretory system. 



The characteristic feature of the excretory system in the two species of 

 echinostomes is the triplet of flame cells at the anterior part of the system. 

 A detailed study of the flame cells in C. biflexa is found in figure 138. The cells 

 are situated in the pockets communicating with the ultimate part of the re- 

 flexed tubule. Cell a is found in the sinus between the secondary and tertiary 

 vessel. It points upward and outward. It is the smallest of the three cells. 

 Cell c occupies the swollen end of the tertiary vessel. It is the largest of the 

 three vessels; its cilia are the most rythmical of the group. Ceil b lies midway 

 between cells a and c. It points downward and inward. Cells a and b func- 

 tion in bringing the excretory wastes into the vessel from the surrounding 

 tissue and cell c directs the excretory material along the vessel. 



The excretory system of certain species of echinostome cercariae contain 

 granules. These granules have been found in all C. trisolenata examined; 

 they are found in the lateral vessels from the region of the pharynx posteriad 

 to the acetabulum. They have not been seen in C biflexa. 



The excretory system in the tail of echinostome cercariae is not uniform. 

 In C. trisolenata there is a single median tube with no prominent tributaries. 

 In C. biflexa a median tube runs two-fifths the distance posteriad, where it 

 divides to form two tubules which proceed distad. In C. trivolvis and C. 

 reflexae (Cort, 1915, Figs. 39, 43) the median vessel of the tail courses back- 

 ward about one-fifth way and ends there in a bifurcation, the ends of which 



