37] LIFE HISTOR Y OF TREMA TODES—FA UST 37 



The excretory system in the tail of monostomes is simple. It consists 

 of a median tubule, with tributary laterals, which swell in the proximal 

 region and empty into the common bladder of the trunk. 



B. Holostomata. The excretory systems of Holostomidae and Hemi- 

 stomidae are sufficiently different to require separate treatment. 



1. Holostome type. No accurate or detailed description of the tetracotyle 

 type of excretory system exists. De Filippi (1857, Fig. 26) has pictured two 

 laterals for C. vesiculosa, arising from nimoierous tubules in the anterior part 

 of the body. The connection of these tubes in the region of the bladder is not 

 clear. Altho his sketch was made ''to show particularly the lateral vessels," 

 it gives no adequate conception of the fundamental vessels of the system. 

 Brandes (1891:569) merely states that the "system reaches into all parts of 

 the cone; an especially large canal passes longitudinally thru the anterior wall 

 of the cone. " Only a faint suggestion of the system is figured by Rosseter 

 (1909, Fig. 17), for Holostomum excisum (von Linstow). Brown (1899, Fig, 

 11) has worked out an interesting but unusual type. In view of the lack of 

 definite data concerning the excretory vessels of the holostomid group, it 

 seems advisable to describe the system for the species Cercaria flabelliformis. 



The excretory system of Cercaria flabelliformis is shown in figure 39. At the 

 extreme posterior end of the worm, situated slightly dorsally, is the excretory 

 pore. It is the opening of a relatively small bladder no larger than the pore 

 itself. At its antero-lateral horns two large trunks arise, considerably inflated 

 in their posterior portion. They may be traced forw^ard along the inner 

 reaches of the digestive ceca until they reach a place about two-fifths the dis- 

 tance from the anterior end of the larva. Here a transverse canal is found, 

 with a median connection between the two trunks, and lateral transverse 

 tubules. The lateral tubules drain the part of the larva posterior and lateral 

 to them. Between them and the main longitudinal trunks are found a great 

 number of anastomoses. Anterior to the median transverse canal the tubules 

 spread out in fan-like arrangement, running to the sides and front of the worm. 



Apparently this system was originally distome in character, but was made 

 over to suit the needs of a modified distome larva. The longitudinals are 

 clearly those of the Y-type so common to the excretory system of the distomes. 

 On the other hand, the transverse tubes and the anastomoses of the postero- 

 lateral reaches are new structures. 



The entire system is filled with minute refractory granules which facilitate 

 the tracing of the courses of the various vessels. 



2. Hemistome type. This type has been worked out in faithful detail 

 both in the larva (Diplostomulum) and in the adult. Hence a discussion of 

 the excretory system of C. ptychocheilus will be limited to the points of diver- 

 gence from the previously described species. 



The earliest larvae of this group to be accurately figured are Diplostomulum 

 clavatum (Nordmann) and D. volvens (Nordmann) (1832, Taf. II-IV). From 

 the elongated bladder there arises a bicornuate structure which proceeds 

 forward and outward for a short distance. A bifurcation of each cornu then 



