477] LARVAL TREMATODES—CORT 31 



DISTOME CERCARIAE 



The great bulk of known cercariae belong to this division. In ray 

 material are eleven distome cercariae representing eleven of the principal 

 sub-groups. 



GYMNOCEPHALOUS CERCARIAE 



Since beyond the fact that they develop in rediae the cercariae 

 placed in this subdivision agree only in the absence of certain characters, 

 it is without doubt an unnatural group. However in the present state of 

 our knowledge it is convenient to retain it. Of my material only Cer- 

 caria megalura belongs here. This species and its allies differ so much 

 from all the other cercariae of the gymnocephalous group, that I pro- 

 pose to make them the basis of a new sub-group, to which the name 

 Megalurous or heavy-tailed cercariae may be given. 



MEGALUROUS CERCARIAE 



From 73 specimens of Pleurocera elevatum from the Sangamon 

 river near Mahomet, Illnois, examined during November and December, 

 1913, one was found with the liver packed with rediae in which devel- 

 oped a very peculiar kind of cercaria. Comparison showed this form 

 to be the same as the larger cercaria which Cary assigns to Diplodiscus 

 temporatus. Since Cary's account is not very complete, obscured by a 

 mistaken viewpoint, and incorrect in many particulars, a further de- 

 scription of this species seems advisable. Altho many of the cercariae 

 seemed fully matured, none were found free in the organs of the snail 

 and no rediae were found which contained rediae. 



Living rediae and cercariae of Cercaria megalura moved actively. 

 The redia was very active and the region back of the posterior locomotor 

 appendages on account of its mobility and attenuation resembled a tail. 

 The anterior portion of the body also could be extended and contracted 

 freely and with the aid of the locomotor appendages locomotion was 

 possible. The cercaria was unable to use its tail for swimming in open 

 water but on a substratum it moved fairly rapidly with the aid of the 

 suckers. With the acetabulum attached the anterior end would reach 

 out and the oral sucker take hold. The acetabulum would then loosen 



