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fwa 



FlO. 'i()2. Nereis. Later stages iu the development. A, stage at which the pr>itu( inch and the 

 apical tuft of cilia first become distinct. B, somewhat later stage, in which the stomodaeal 

 invaginaticm is being formed, and the rudiments of the mesoderm bands are distinct ; C, late 

 trochophore stage, in which there are rudiments of the setigerous sacs ; D, somewhat later 

 stage, in which the parapodia have begun to become prominent and the provisional setop 

 project freely ; E, larva with three segments, an. anus ; ap. oil. apical cilia ; ap. pi. apirnl 

 plate ; eye, eye ; fr. bod. frontal bodies ; int. intestine ; /. mus. longitudinal muscle ; mes. 

 mesoderm ; mo. mouth ; neur. pi. neural plate ; para, parapodia : pin. ar. pigmented area ; 

 prot. prototroch ; sens. h. sensory hairs ; set. sacs, setigerous sacs ; .w>. second somatoblast 

 and group of cells formed from it ; st. stomoda3um ; tent, peristomial tentacles. (After 

 E. B Wilson.) 



442 



