34 ILLINOIS BIOLOGICAL MONOGRAPHS [34 



of the pharynx. They open thru long-necked ducts into the oral pocket. The 

 glands are in masses; they vary in the number of cells from four in each lateral 

 mass of some furcocercariae (Fig. 144), to eight or ten in the stylet cercariae, 

 while in the echinostomes they run as high as 110 on each side of the esophagus 

 (Fig. 134). In general the cells are characterized by a densely staining gran- 

 ular protoplasm and a highly refractive nucleus, which remains hyaline when 

 treated with hematoxylin dyes. Most interesting is the type presented in 

 Cercaria crenata (Fig. 55), where there is a differentiation of inner and outer 

 groups of the glands on each side of the gut. These groups have individual 

 canals to their exit at the oral pocket. The outer series consists of six glands, 

 comparatively small, 8^ to 9ij. in diameter, goblet-shaped, extending caudad 

 to the midacetabular region. They are finely granular and are best studied 

 in living mounts. The inner series consists of five cells, two of which are 

 situated just behind the pharynx and the other three postacetabular, thus 

 causing the inner series to be divided into an anterior and a posterior group. 

 These inner gland cells are ll/i to ISfx in diameter, and coarsely granular. 

 Their difference in structure suggests a functional difference. 



The mucin glands of the redia of C. flabelliformis are paired structures, 

 lateral and dorsal to the digestive pouch, consisting of a single series of six 

 cells which open thru a common tube into the pharynx region of the redia. 

 The cells are similar in structure to the mucin cells of the cercariae of other 

 groups, altho no such glands have been recorded from the cercariae of the 

 holostome group. Only one other case has been reported for the redia, that 

 for the parthenita of Cercaria equitator by Ssinitzin (1911:52, Fig. 50). In 

 this redia the gland cells consist of a single cell with a wide duct to the pharynx 

 region. A similar pair of unicellular salivary glands is figured by Looss for 

 the miracidium of Schistosoma haematobium (1896, Fig. 113, glcph) and by 

 Miyairi and Suzuki for the miracidium of S. japonicum- (1914, Taf. 2, Figs. 

 1,2). This occurrence of the mucin glands in the miracidium, redia, and cercaria 

 of various groups, and the fact that they pass into the intermediate host along 

 with the larva (La Rue, 1917), show that these organs are of fundamental 

 importance in the economy of the worm. 



That these glands are of more specific character than the ordinary saHvary 

 and epidermal cells of the trematodes is demonstrated by their differential 

 staining reaction. The usual hematoxylin dyes show a great number of 

 granular protein inclusions. Recently La Rue (1917) has shown that these 

 glands in Cercaria marcianae have "mucus" in their ducts, because of the 

 staining reaction with toluidin blue and thionin. However, since the glycopro- 

 tein of salivary digestion is mucin (Mathews, 1915:323), it is more exact to 

 designate these structures as mucin glands. 



A type of gland undoubtedly common to all cercariae is the cystogenous 

 gland. It is a unicellular organ in the parenchyma just beneath the integument. 

 In some groups this cell may be small and in the midst of parenchyma 

 cells (C glandulosa, Fig. 62). In other groups the cystogenous cell is very 

 large and conspicuous as in the species C. pellucida (Fig. 14), C. dendritica 



