457] LARVAL TREMATODES—CORT 11 



MONOSTOME CERCARIAE 



About five per cent., of the largest specimens of Physa gyrina 

 from a drainage ditch north of Urbana, Illinois, examined in December, 

 1913, were infected with the rediae and cercariae of a monostome. I 

 propose to name this species Cercaria urbanensis. The infection was in 

 the liver of the snail and there were present both rediae in different 

 stages of development and free cercariae. No sporocysts were found 

 and none of the rediae contained rediae. It is interesting to note that 

 in the descriptions of monostome larvae no mention is made of sporo- 

 cysts, and only one observation of rediae developing from rediae. 

 Braun (1892:805-806) notes that in certain of the monostomes rediae 

 are already developing in the free swimming miracidia, which he con- 

 siders to already represent sporocysts. Looss (1896:197) states that 

 in material of Cercaria imbricata Looss collected from Bythinia ten- 

 taculata near Leipzig, rediae were present in which rediae were devel- 

 oping. From this he concludes that the life-history of this species is 

 accomplished in the same manner as that of the amphistomes, which 

 have several generations of rediae. 



When freed from the liver of the snail the redia had considerable 

 power of extension and contraction. The immature ones especially 

 stretched out the anterior end and reached in all directions. No loco- 

 motor appendages were present either in young or mature redia and 

 no locomotion was noted. In fact the redia of Cercaria imbricata Looss 

 is the only monostome redia that is reported with locomotor append- 

 ages. According to Looss (1896:196) the appendages in this species 

 were well marked in the young redia but more or less effaced with 

 advancing age. In some of the largest rediae of Cercaria urbanensis 

 very peculiar annular constrictions were noted in different parts of the 

 body, which divided it into two or three separate regions connected by 

 very narrow passages (Fig. 12). These constrictions seem to be due 

 to temporary unequal contraction states in different regions of the 

 circular body muscles. This condition for the redia of Cercaria urban- 

 ensis was observed only in preserved material. Leidy (1877:200; 

 1904:143-144) notes such constrictions in the living redia of a mono- 

 stome cercaria which he calls Monostoma lucanica. 



