494 University of California Piiblications in Zoology [Vol. 18 



ing the tubes of the excretory system, which can only be followed with 

 difficulty. In the main stem of the tail (fig. 1, st) there are two 

 lateral rows of large, fairly regular nuclei. The tail is an effective 

 muscular organ and is so attached that it is readily lost when the 

 cercaria starts to penetrate into its final host. 



The ventral sucker (figs. 1, 2, s) is located at a point about three- 

 fourths of the distance from the anterior to the posterior end of the 

 body. It is circular in ventral view with a depth considerably greater 

 than its diameter (fig. 2). In the living animal the ventral sucker 

 can be protruded so that it has almost the appearance of a proboscis. 

 The sucker functions strongly in locomotion and is able to hold the 

 cercaria against considerable pressure. 



I have already given in a previous publication (Cort, 1917, p. 52) 

 a preliminary description of the excretory system of the cercaria of 

 8. japonicum. The bladder (figs. 1, 2, h, ht) is composed of elongate 

 tubes and extends from the body into the tail. As in all fork-tailed 

 cercariae I have ever observed, there are two excretory pores (fig. 1, 

 exp), one on each of the divided lobes of the tail. The sides of 

 the V-shaped, bladder tubes of the body unite at the posterior end and 

 pass into the main stem of the tail as a single tube, which divides to 

 send branches to the pores at the tips of the bifurcations of the tail. 

 At the pores the tubes are slightly enlarged (fig. 1, exp). There is a 

 characteristic anastomosis in the tube of the bladder just where it 

 enters the tail, forming a little island (fig. 1, i). The bladder in the 

 body (figs. 1, 2, &) which after the loss of the tail becomes the bladder 

 of the adult, is V-shaped. The sides of the V extend from their point 

 of union at the posterior end of the body along the ventral surface 

 to a region in front and to each side of the ventral sucker. They then 

 turn dorsad and pass along the sides of the cercaria still in the super- 

 ficial laj^er of parenchymatous tissue to the points on each side where 

 they receive the anterior and posterior collecting tubes (fig. 2, act, 

 pet). Two ciliated areas (fig. 2, ca) are present on each side near the 

 ends of the sides of the bladder. The collecting tubes (figs. 2, 3, act, 

 pet) are short and each receives the capillaries from two flame cells, 

 making four flame cells on each side, three in the body and one in the 

 anterior part of the stem of the tail (figs. 2, 3, /). The positions of 

 the flame cells are clearly indicated in figure 2. . The complete 

 excretory system of the cercaria of 8. japonicum is shown diagram- 

 matically from the ventral side in figure 3. The cercaria of 8. japon- 

 icuni has the smallest number of flame cells that I have ever observed 



