32 ILLINOIS BIOLOGICAL MONOGRAPHS [478 



its grip, arid the body contract until the suckers were close together. 

 The acetabulum would again take hold just back of the oral sucker, 

 which would in its turn become loosened and extended. Locomotion 

 consisted in a continued repetition of these movements. During this 

 process the tail was contracted and took no part in the movement. At 

 certain times a cercaria became attached by the posterior tip of the tail, 

 which is furnished with an adhesive organ. The animal then extended 

 to five or six times its usual length, and became greatly attenuated. 

 While in this position the cercaria moved continually with a wriggling 

 \/ motion. Looss (1896:202) noted a similar activity in Cercaria distoma- 



tosa Sonsino from Cleopatra bidimoidcs Bourg., from Cairo, Egypt, a 

 form very much like Cercaria megalura. This cercaria became attached 

 by the extremity of the tail to the surface of the water or to some bodies 

 such as plants or branches of trees very near the surface of the water, 

 and moved in a serpentine manner like a tubificid worm. This compari- 

 son would apply equally well to Cercaria megalura. What relation this 

 peculiar habit has to the future development of the cercaria is not 

 known. 



No cercariae were found encysting altho large numbers had ex- 

 truded cystogenous material in the form of a sort of open tube around 

 the body (Fig. 30). In fact this seemed to be the normal procedure 

 when the animal came in contact with fresh water. Cary (1909:609- 

 610) performed experiments with some of his specimens of Cercaria 

 megalura which showed that this extrusion of cystogenous material was 

 due to the change from the conditions in the liver of the snail to fresh 

 water. Looss (1896:201-203) found no free individuals of Cercaria 

 distomatosa in which the cystogenous material was still in the glands, 

 and he also mentioned that when the cercariae were taken up in a pipette 

 they became encysted as quick as a flash. He noted further that they 

 encysted also in the open, loosening their hold and dropping to the 

 bottom after having lived for a period free. 



The redia (Figs. 31 and 36) of Cercaria megalura is an elongate sac 

 slightly tapering toward the anterior end, with the posterior locomotor 

 appendages about six-sevenths of the distance from the anterior to the 

 posterior extremity. It is widest just in front of the appendages and 

 tapers almost to a sharp point posteriorly. The birth pore is on the 

 dorsal side just back of the pharynx. 



The mouth of the redia is at the anterior tip and the oral cavity 

 opens into a short, narrow passage, which widens out almost immediately 

 into the voluminous digestive tract. This extends back of the posterior 

 locomotor appendages nearly to the end of the body. In cross sections 

 (Fig. 35) the intestine occupies from one-third to two-thirds of the body 



