66 ILLINOIS BIOLOGICAL MONOGRAPHS [66 



species the suctorial pocket is hemispherical with the opening ventral. The 

 lateral accessory suctorial grooves in T. pipientis are non-muscular oblique 

 slits; in C. flabelliformis they are at first oval depressions which are modified 

 later into a pair of lateral lappets. The primitive genital pore in C. flabelli- 

 formis is 0.05 nam. in diameter; in T. pipientis it is 0.08 mm. wide, with a 

 crown of heavy spines. The homologies between the lateral excretory trunks 

 of the two species are apparent, altho the median transverse trunk is much 

 farther anterior in T. pipientis than in C. flabelliformis. The tributary tubules 

 are entirely different in the two species. The digestive ceca of the Bitter 

 Root species conform to the family type in extending well into the posterior 

 part of the body; those of T. pipientis are short and rudimentary. The geni- 

 tal organs of the two species occupy the same relative position, altho individual 

 variations in size and shape of organs are evident. 



In concluding the study of the tetracotyle larvae, emphasis must be placed 

 on the maturation of the parthenogenetic ova, which shows that these larvae 

 do not develop in miracidia, without the intercalation of parthenitae as 

 Brandes (1891:572) and Fantham (1916:224) believe. This fact, previously 

 recorded by the writer (1917), makes the morphological evidence complete 

 in support of the view of true alternations of hermaphroditic and partheno- 

 genetic generations among Holostomata. 



Cercaria ptychocheilus Faust 1917 



This form, really a Diplostomulum, is elongate ovate in outline, with dorso- 

 ventral flattening, slight ventral concavity, and a more or less distinct sepa- 

 ration of body into anterior and posterior portions. In addition, the 

 group to which this worm belongs lacks the lateral auxiliary sucking grooves 

 which are characteristic of the tetracotyle forms. Several species of Diplosto- 

 mulum have been well described and their excretory system beautifully traced 

 by von Nordmann (1832). These include the species Z>. volvens,D.cuticula, 

 D. clavatum, and D. brevicaiidatum. Of the forms found in North America 

 there have been recorded D. cuticula, D. volvens, and D. grande of the Old 

 World species, and D. parvidiim (Stafford), new to North America. However, 

 as has been previously suggested, none of these American records give suf- 

 ficient data to distinguish accurately the species. 



The general outline of the body of Cercaria ptychocheilus is such as to dis- 

 tinguish it readily from the described species. Broadly oblong-ovoid in 

 contour, with the anterior half laminate and the posterior portion fleshy, 

 this cercaria might at first be confused with distome cercariae. Such a con- 

 fusion is caused, further, by the abbreviated appendiculate portion of the 

 larva, which, on extension into a caudal cone, may reach one-third of the body 

 length, but on contraction barely protrudes behind the anterior part of the 

 body. The concavity of the anterior part is found only in the fleshy region 

 behind the acetabulum. Here in this area is found the muscular complex 

 comparable to the cup-shaped suctorial apparatus of the tetracotyle. 



