1920] Johnson: Life Cycle of Echinostoma Revolutum (Froelich) 355 



the base of the body to the end of the tail the excretory tubules bend 

 almost at right angles and empty laterally. Figure 42 shows the 

 right half of this primitive muscular bladder in various shapes, drawn 

 within a few seconds of each other. These swellings or bulbs give 

 evidence of a process similar to peristalsis in the elimination of 

 excretory waste and show that in this early stage the bladder is quite 

 muscular. When the embryo is 0.710 mm. long the final shape of the 

 cercaria is nearly attained. At this stage the union of the two tubules 

 of the primitive muscular bladder is partially accomplished (fig. 40) 

 just at the juncture of the body and tail. In cercariae 0.765 mm. in 

 length (fig. 41) the process of union is nearly completed, extending 

 both into the body and tail. Thus the tubule found in the fail of 

 mature cercariae is really a part of the bladder. Principally upon 

 similar data in regard to the development of the bladder tubules in the 

 tail, Ssinitzin (1911) based his theory that the body proper of many 

 cercariae really extends to the region of the excretory pores in the 

 tail and not to where the slender part ordinarily called the tail joins 

 the body. He then holds that the true tail is an outgrowth from tissue 

 found just posterior to and between the excretory pores. There is 

 considerable evidence, aside from the work of Ssinitzin, to uphold this 

 theory. Looss (1896, figs. 147, 155, 172, 173, 174) shows that in both 

 monostomes and distomes such a formation of the bladder takes place. 

 Also Looss (1892, pi. XX) shows several stages in the development of 

 an amphistome cercaria portraying the same development of the 

 bladder. From this evidence it seems to me quite logical to say that 

 the body proper of such cercariae extends to the excretory openings 

 on the side of the tail and that the true tail extends only from this 

 point on. 



Since the bladder sac is derived from the union of two tubes in the 

 embryo, then certainly, if necessary, they could unite for a longer 

 distance and form a much larger bladder. Also since the muscular 

 descending tubes (1c) have the power of contraction and expansion 

 it is obvious that to limit the bladder to the muscular sac is not correct. 

 Also since the concretional tubes of the bladder (Id) are continuations 

 of the muscular tubes (lc), and since the ascending tubes (lc) are 

 directly continuous with the concretional tubes (Id), then it would 

 appear to follow that all these parts form the complete bladder. 



No record can be found of the complete analysis of the excretory 

 system at any stage of an echinostome. The nearest approach is the 

 work of Looss (1894, fig. 191). in which he describes this system of 



