41] LIFE HISTORY OF TREMATODES— FAUST 41 



open to the sides. The hiflexa type seems to be intermediate between the 

 echinostome type described by Cort and the more common distome type. It 

 is highly probable that the excretory system of the echinostome, with three 

 flame cells in the anterior portion of the system and possibly several smaller 

 ones further caudad, has arisen from the primitive distome type. In most 

 cases, the posterior flame cells have become fused into larger ones, so that only 

 three flame cells remain in the anterior part of the system in C. trisolenata and 

 C. biflexa. 



3. The Furcocercaria type. The mature apharyngeal distome cercaria 

 of the furcocercous type (i.e. schistosome) has a very small bladder in the 

 posterior part of the body and two lateral vessels running cephalad. The 

 unpaired portion of the tail has a single median canal, which is united to the 

 system of the trunk thru an "eyelet anastomosis." The median tubule of 

 the tail forks to enter the rami. The origin of the caudal vessels has been 

 worked out by Looss (1896, Figs. 172-174) for C. vivax Sonsino. These tubules 

 arise as the posterior extension of the paired body excretory tubes. Their 

 fusion in the common portion of the tail occurs after the rami have become 

 well differentiated. The "eyelet" is an index of the original paired system 

 in both body and tail. 



A study of the species C gracillima (Fig. 143) and C. tuberistoma (Fig. 155) 

 shows the main features of the vivax type. The small bladder, the lateral 

 canals, the median caudal tube, bifurcating distally to proceed into the rami, 

 the "eyelet" at the junction of the body and the tail — all of these seem to be 

 constant for the entire group. Beyond these characters the features of the 

 several species are divergent. 



In C. gracillima (Figs. 143, 145) the caudal portion is extremely simple, 

 containing only the common median tubule and the forked tubule system 

 entering the rami. Unlike C. vivax with its three pairs of flame cilia in the 

 common caudal tubule, this species has no flame cells in the caudal portion 

 of the worm. The system in the body of the cercaria has a non-muscular 

 trilateral bladder, small posterior tubes arising from the lateral tubes, and 

 a ciliary pocket about one-fourth way from the posterior margin of the body, on 

 the inner wall of each lateral tube (Fig. 145). At the posterior margin of 

 this ciliary pocket small tributary canals from the median plane flow into the 

 main canal. Slightly cephalad is another pocket, somewhat larger than the 

 ciliary pocket, filled with small granules of various sizes and shapes. Into 

 this pocket four or five small canals empty, the median ones of which anstomose 

 with their mates from the opposite side. No ciliary cells have been found in 

 the terminations of the capillaries. 



In C. tuberistoma the caudal portion of the worm is characterized by five 

 transverse canals. Another pair, anterior to these, is conspicuous because 

 it runs forward for a short distance and is then reflexed backward for some 

 distance (Fig. 155). The eyelet and the bladder are both muscular. In the 

 body portion there are no pockets for the lodgement of granules and no 

 transverse anastomoses. No flame cells have been found in this larva. 



