BY R. J. TILLYARI). 



617 



The Caudal Filaments of the Plectoptera. (Text-fig.43). 



The larvie of the May Flies or Plectoptera possess thiee caudal 

 processes, viz., the two latero- ventral cerci, and the single median 

 dorsal ap])endix dorsa/is. Thus the former are the homologues 

 of the lateral caudal gills of the Zygopterid larva, while the 

 latter is the homologue of tlie median caudal gill. 



All three of these filaments closely resemble those of the 

 Perlaria externally, being long, slender, and manv-jointed. 



Text-fig.43. 

 T.S. tlirough the three caudal filaments of a well-grown Pleotopterous 

 larva, Atatophlehia sp, Letteiing as in Text-fig. 42; AD, appendix 

 dorsalis; C, eercus; rh, ventral blood-canal; ( x 130). 



In transverse section (Text-fig.43), the structure of these organs 

 is of great interest. In all three, the transverse section is 

 circular, the cuticle and hypodermis fairly thick, the latter with 

 many closely arranged nuclei, and the interior an open prolonga- 

 tion of the hsemocoele, as in the filaments of the Perlaria. Beyond 

 this, the cerci differ so much from the appendix dorsalis that we 

 must deal with them separately. 



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