79] UFE HISTORY OF T REM ATODES— FAUST 79 



and 0.13 mm. to 0.15 mm. in width. The tail is at least as long as the body 

 or slightly longer. Its width is about 0.05 mm. at the base. The oral sucker 

 has a diameter of 55At and the ventral sucker, situated at the beginning of the 

 posterior third of the body, measures 65/* in diameter. Around the oral hood 

 is a circlet of collar spines, 42 in number, ovoid elongate, bluntly rounded at 

 both ends, with a length of 10/t to 15/1 and a thickness of 3/i. 



The worm was found in Physa gyrina in November 1916, and in Planorhis 

 trivolvis in May 1917, in the neighborhood of Buckhouse Bridge, near 

 Fort Missoula, Montana. 



The parthenita is a redia with a length measurement of 0.4 mm. and a 

 thickness of 0.088 mm. (Fig. 137). The locomotor feet are short, blunt pro- 

 cesses in the posterior third of the body, and have a gross span of 0.1 mm. 

 In contrast to the large gut-pouch of Cercaria trisolenata parthenitae, the 

 rediae of this species have short inconspicuous rhabdocoel guts, only 0.1 mm. 

 in length. One-third of this is occupied by the pharynx. The body wall 

 is covered with a thick integument, within which is a heavy muscular layer. 

 At the posterior end are a number of small spinous projections (Fig. 141). 

 The germinal epithelium also is at the posterior end. A noticeable feature 

 of the cleaving ova is their flattened condition (Fig. 141). Stages in matura- 

 tion and cleavage are seen in this figure and may be compared with similar 

 stages of maturation and development in C. trisolenata (Fig. 140.) The cer- 

 cariae, when mature, escape thru the birth-pore situated ventrolaterad. 



A prominent excretory system is foimd in this cercaria (Fig. 135). The 

 vesicle is a cylindrical organ inflated posteriorly. It is not muscular to any 

 marked degree. Tubular cornua empty into the anterior end of the bladder. 

 As these cornua are traced forward lateral tributaries are found to empty 

 into them at regular intervals. In the region of the pharynx the tubes become 

 attenuated and bend twice upon themselves (Fig. 138) . The detailed descrip- 

 tion of this anterior end of the system of Cercaria biflexa is found in the section 

 on morphology (p. 40). It may be noted here that there are three flame cells 

 along the course of the ultimate tubule of the system, and that these seem 

 comparable to the three flame cells found in C. trisolenata. The excretory 

 tube in the tail is a single median tube for about two-fifths of the way distad, 

 at which point it forks and continues double the remainder of the way distad, 

 with numerous cross-anastomoses. It does not open to the outside either 

 on the sides or end. 



The digestive system consists of an extremely long esophagus, extending 

 all the way to the acetabulum; furcae which end at the caudal end of the 

 animal; and salivary-mucin glands, developed to a very high degree. These 

 latter consist of an inner and an outer series of right and left groups (Fig. 134). 

 There are from fifty to sixty cells in each group, in oblong clusters, with a 

 common duct anterior to each series leading cephalad. The two ducts of each 

 side fuse to form a single lateral duct which leads into the oral pocket. These 

 glands are different from the majority of mucin glands in being differentiated 



