36 ILLINOIS BIOLOGICAL MONOGRAPHS [36 



lashed from side to side, until finally a more vigorous movement detaches 

 it. The whole process is very rapid, and in a few minutes a layer of consid- 

 erable thickness is formed, whilst its substance begins to harden. " 



EXCRETORY SYSTEM 



The excretory system is the most dehcate of the four important systems 

 o the trematode. It can be worked out with precision in the Uving animal, 

 but in preserved material it is impossible to find more than the main trunks 

 of the system. In all of the cercariae and parthenitae described in this paper 

 the excretory systems have been studied from living material. Altho there 

 are many individual differences within groups, yet the fundamental uniformity 

 of groups is evident. 



A. The Monostomata. The main features of the excreton,-^ system of the 

 Monostomata are the two main trunks arising from a common point just behind 

 the median eye-spot or median pigment center, and proceeding posteriad and 

 laterad to the posterior part of the body, where they join one another in the 

 common vesicle. The bladder opens to the outside thru the excretory pore, 

 which is not terminal but slightly dorsal. 



The main excretory trunks are filled with large refractor}' granules, more 

 extensively described on p. 42. The continuous circuit of the system provides 

 for the transfer of granules and other waste products from right to left and 

 reversely, dependent on the contraction and expansion of the several parts of 

 the animal. 



The bladders of the various species differ considerably in size and structure, 

 but as a whole they may be placed in two sub-groups. In the trioculate forms, 

 such as Cercarin pdlucida, in dorsal view the bladder is distinctly trilateral 

 when relaxed, with the excretory pore at the posterior horn. This same type 

 is found in C. ephemera Nitzsch (Ssinitzin, 1905, Fig. 76), and in C. imbricata 

 Looss (18%, Fig. 148), and also in C. zostera (Ssinitzin 1911, PI. 1, Figs. 14, 

 15). 



In action, however, due to the muscular movements of the posterior portion 

 of the body, the anterior portion of the bladder may seem to be a separate 

 organ opening into the bulbous posterior portion of the vesicle thru a con- 

 stricted area. In the binoculate tj'pes, on the other hand, the bladder is spheri- 

 cal, with the excretory trunks emptying into the extreme lateral reaches of the 

 vesicle. The excretory pore in these species is subterminal rather than termi- 

 nal. The only binoculate species known are C. lophocerca (de FiUppi, 1857, PI. 

 1, Fig. 3), C. itrbanensis (Cort, 1915, Fig. 5), and C. konadensis. Lebour 

 (1907:443, PL X, Fig. B) describes the bladder of C. lophocerca as semilunar, 

 but from her figure it appears more reniform than lunar. Cort does not 

 describe the shape of the bladder of C. urbanensis, or state its size. The writer 

 has found it to measure 50/i to 60/i in median sagittal line and 60ju in transverse 

 section for preserved material. The excretor)'^ pore of this species is large, 

 some 20^1 in diameter; it is weakly muscular (Fig. 35). In C. konadensis (Fig. 

 29) the bladder is smaU, 14)ii to IS/x in diameter. The excretor)' pore is cor- 

 respondingly small, 3n to 4^i in diameter, and weakly muscular. 



