THE PROCTUCHA. 



if;:, 



cles are developed on the head in front of thepwe-oral ciliated 

 band. But, as development advances, the segmentation be- 

 comes obliterated, tin- ciliated bands and the feelers vanish, 

 and the worm assumes the characters of a Nemertean. 1 



Fro. .r 



. IT, 



Fio. 36. 



FIG. 35-37. Pilidium gyrans (after Leuckart and Pagenetecher). 



35. Young Pilidium : o, alimentary ranal : 6, rudiment of the Nerocrtean. 



36. Pilidium with a more advanced Nemertean. 



37. Newly-freed Nemertean. 



In species of the genus Lineus, the ciliated embryo which 

 leaves the egg is speedily converted into a body like a helmet 

 with ear-lappets, and having a tuft of cilia in place of a plume 



1 It is very probable, however, that this larva belongs to thejjenus Myyor- 

 dius, which appears to be an aniuvti'nt form between the Turbellaria and other 

 groups. See Schneider, " Ueber Bau und Entwickelung von PolygordiuB." 

 (** Archiv fur Anatomic und Physiologic," 1868.) 



