72 ILLINOIS BIOLOGICAL MONOGRAPHS [72 



sporocyst is that the germinal epithehum is not localized; consequently germ 

 balls may be derived from any portion of the body. Whether or not the germ 

 cells arise parthenogenetically has yet to be determined. This type of germ 

 ball production represents a structural simplicity previously not recorded for 

 the sporocyst. 



The excretory system differs from that of other stylet cercariae mainly 

 in the shape of the bladder and of the essential tubes. The bladder is small, 

 heavily muscular, flattened antero-posteriad. Leading out from it in a median 

 plane is a non-muscular shank of some length, which opens into two cornua 

 a considerable distance in front of the bladder. Caudad these cornua are 

 vesicular, but further cephalad they become constricted into a system of 

 tubules similar to those of C. glandulosa, which run thru the body to collect 

 the excretory wastes. 



The digestive system consists of a long esophagus, with pharynx at the 

 anterior end, and a wide bifurcation somewhat anterior to the acetabulum. 

 The entire digestive tract is very attenuate in outline. It is not supplied 

 with glands along the furcae but has an even more abundant supply 

 than C. glandulosa in the region of the pharynx (Fig. 76). Altho the pharynx 

 itself measures only ISfx in cross section, the glandular area as a whole em- 

 braces a sphere 65/x in diameter. The rest of the tract is free from gland 

 cells of this nature. The salivary-mucin glands are situated in the upper outer 

 reaches of the furcae. Each group consists of eight cells, relatively very small, 

 granular, with a common duct system opening into the oral pocket. 



The genital organs are similar to those of C. glandulosa (Fig. 78). They 

 differ from the genital cell masses of that form in the more limited vitellaria, and 

 the more conspicuous Laurer's canal. This form is probably a Plagiorchid larva. 



Unlike C. glandulosa this cercaria is slow to drop its tail and much slower 

 to encyst, in spite of the fact that there is an equally good pair of posterior 

 locomotor pockets with spines and an equally good supply of cystogenous 

 material. We have here, then, evidence of a physiological adaptation to 

 different conditions of the environment, where the structure of the two t>pes 

 would lead one to expect similar habits and reactions. 



Cercaria dendritica Faust 1917 



Cercaria dendritica is a species of cercariae readily recognized by its obovate 

 structure, large suckers, large muscular pharynx, and large muscular excre- 

 tory vesicle. The body as a whole is heavily muscular. The tail is short 

 and almost conical (Fig. 81). The body measures 0.33 mm. to 0.4 mm. in 

 length by 0.13 mm. to 0.17 mm. in width. The tail is about half the body 

 length, 0.16 mm. and is 0.04 mm. wide at the base. It is inserted into a typi- 

 cal caudal pocket, the whole cavity of M^hich is lined with stiff spines. The 

 large oral and ventral suckers are nearly equal in size. The former has a 

 diameter of 62/x and the latter of 60//. The stylet (Figs. 82, 83) is short and 

 stout, heavily reinforced at the shank, with a flat deltoid quill. The quill 



